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SWITCHING  EQUIPMENT 

FOR 

POWER  CONTROL 


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SWITCHING  EQUIPMENT 

FOR 

POWER  CONTROL 


BY 
STEPHEN  Q.  HAYES,  A.B.,  E.E. 


NSTITUTE    ELECTRICAL  ENGINEERS;  SWITCHBOARD    PROJECT     ENGIN 
WESTINGHOU8E   ELECTRIC   *    MANUFACTURING   CO. 


FIRST  EDITION 
SECOND  IMPRESSION 


McGRAW-HILL  BOOK  COMPANY,  INC. 

NEW   YORK:    370   SEVENTH   AVENUE 

LONDON:    6  &  8  BOUVERIE  ST.,  E.  C.  4 

1921 


COPYRIGHT,  1921,  BY  THE 
MCGRAW-HILL  BOOK  COMPANY,  INC. 


TK 


PREFACE 

Switching  equipment  for  power  control  forms  a  very  essential 
part  of  any  plant  for  the  production  or  distribution  of  electrical 
energy.  This  equipment  has  been  aptly  described  as  the  "  brain  " 
of  the  electrical  system  as  it  performs  all  of  the  duties  of  direction 
and  control  that  are  so  vital  to  the  proper  functioning  of  the 
system. 

Information  on  the  subject  of  switchboards  and  switching 
equipment  can  be  found  in  very  condensed  form  in  certain 
electrical  handbooks,  and  specific  data  on  definite  appliances 
can  usually  be  obtained  from  manufacturers.  Articles  in  the 
technical  press  also  furnish  a  certain  amount  of  data  on  this 
subject,  but  there  has  been  no  American  book  dealing  with  the 
general  subject. 

Demand  for  a  book  on  this  subject  has  lead  the  author  to 
undertake  its  preparation  basing  it  largely  on  his  own  articles 
which  had  previously  appeared  in  the  switchgear  and  control 
sections  of  the  "Fenders  Handbook  for  Electrical  Engineers" 
and  in  the  Electric  Journal,  Electrical  World,  Southern  Elec- 
trician, Electrical  Age,  etc.  These  have  been  partly  re-written 
and  brought  up-to-date. 

Manufacturer's  publications  have  been  consulted  freely 
and  some  of  their  descriptive  matter  utilized  bodily  or  reworded 
to  adapt  it  to  this  book.  The  attempt  has  been  made  to  select 
such  information  as  would  be  of  the  greatest  use  to  the  largest 
number  of  readers  and  that  would  embody  standard  practice 
rather  than  special  applications. 

Thanks  of  the  author  are  due  to  various  publishers  for  their 

permission  to  utilize  his  material  previously  published,  and  to  the 

—  o      various   electrical   manufacturers  for  the  data  they  furnished. 

'_2      Grateful  acknowledgment  is  also  made  to  the  author's  many 

j.      friends  and  associates  for  information  supplied  and  suggestions 

as  to  subject  matter  and  arrangements  of  material. 

LU          The  main  object  of  this  book  is  to  furnish  the  actual  switch- 

_j_      board  operator  the  information  that  will  help  him  to  keep  the 

Mr>    equipment  in  his  care  in  the  best  operating  condition,  by  ex- 

0"    plaining  what  should  be  expected  of  the  apparatus  and  equip- 


vi  PREFACE 

ment.     It  will  also  assist  him  in  the  selection  and  installing 
of  new  material. 

The  secondary  object  is  to  help  the  student  of  electrical 
engineering  in  a  technical  school  to  get  a  better  understanding 
of  this  branch  of  the  art  and  to  appreciate  how  the  switching 
equipment  ties  together  the  various  generators,  transformers, 
feeders,  etc.,  that  make  up  the  component  parts  of  a  generating 
and  distributing  system. 

Consulting  engineers  and  others  will  find  enough  of  the 
theoretical  features  to  give  them  an  understanding  of  the  func- 
tions and  limitations  of  the  various  devices.  Such  an  under- 
standing will  facilitate  specifying  equipment  that 'can  be  readily 
obtained  and  that  will  operate  satisfactorily  under  actual  con- 
ditions. 

The  arrangement  of  this  book  has  been  based  on  the  idea  of  first 
describing  the  switching  apparatus,  approximately  in  the  order 
in  which  the  various  devices  were  developed.  This  is  followed 
by  considering  the  main  connections  desired  in  a  power  plant 
and  the  means  for  carrying  out  the  connections  so  as  to  obtain 
the  maximum  amount  of  security  and  flexibility  with  the  mini- 
mum outlay.  Switchboard  panels,  control  desks,  etc.,  are 
considered  next  with  the  location  of  breakers,  bus  structures, 
etc.,  and  the  general  arrangement  of  the  part  of  the  power  plant 
devoted  to  switching  equipment. 

Description  of  apparatus  has  been  confined  almost  exclusively 
to  present  day  standards  to  keep  the  subject  matter  down  to  a 
reasonable  length,  but  a  few  references  have  been  made  to  some 
of  the  older  types  of  apparatus  to  show  the  progress  of  design. 

American  practice ,  forms  the  basis  for  the  descriptions  and 
most  of  it  is  the  practice  of  the  largest  electrical  manufacturers. 
The  attempt  has  been  made  to  include  descriptions  of  apparatus 
of  other  important  builders,  but  it  has  been  impossible  to  describe 
all  of  the  apparatus  of  all  the  builders.  The  data  has  been 
obtained  from  various  sources  and  the  most  readily  available  ma- 
terial has  been  used. 

STEPHEN  Q.  HAYES. 


CONTENTS 

PAGE 
PREFACE V 

I.  SWITCHES 1 

II.  AUTOMATIC  PROTECTION  AND  FUSES 24 

III.  CARBON  BREAKERS 36 

IV.  OIL,  CIRCUIT-BREAKERS 75 

V.  RELAYS 157 

VI.  SWITCHBOARD  METERS 171 

VII.  INSTRUMENT  TRANSFORMERS 198 

VIII.  LIGHTNING  ARRESTERS 209 

IX.  REGULATORS 233 

X.  INDUSTRIAL  CONTROL  APPARATUS 254 

XI.  SWITCHBOARDS — GENERAL  INFORMATION 267 

XII.  SMALL  D.  C.  AND  A.  C.  SWITCHBOARDS 296 

XIII.  LARGE  HAND  AND  ELECTRICALLY  OPERATED  PANEL  SWITCHBOARDS 
FOR  D.  C.  GENERATORS  AND  ROTARIES 321 

XIV.  HAND  OPERATED  A.  C.  SWITCHBOARDS 360 

XV.  Bus  BARS  AND  WIRING  GENERAL  INFORMATION 381 

XVI.  BREAKER  STRUCTURES 406 

INDEX.    .  .    455 


vii 


SWITCHING  EQUIPMENT 
FOR  POWER  CONTROL 


CHAPTER  I 
SWITCHES 

KNIFE  SWITCHES 

Definition. — Switches  may  be  considered  as  devices  for 
mechanically  opening  up  an  electric  circuit  and  their  design  is 
based  primarily  on  the  following  features:  They  must,  when 
closed,  carry  their  rated  current  without  excessive  drop  or  ex- 
cessive heating  and  must  take  care  of  the  overloads  met  in 
practice;  they  must,  while  being  opened,  be  designed  to  prevent 
or  render  harmless  any  arcs  that  may  be  formed;  they  must, 
when  open,  insulate  all  live  parts  for  maximum  potential  in  a 
permanent  manner. 

Early  Types. — The  earliest  types  of  switches  consisted  of 
metal  plates  mounted  on  wooden  blocks  and  connected  together 
by  a  plug  inserted  between  them.  The  weakness  of  this  first 
design  was  the  proximity  of  the  plates  and  the  tendency  for  an 
arc  to  hold  on  when  the  plug  was  withdrawn.  The  next  step 
was  to  increase  the  distance  between  the  two  stationary  contacts 
and  to  use  a  movable  plate  attached  to  a  handle  for  bridging  the 
gap  between  these  stationary  contacts.  To  avoid  losing  this 
movable  plate,  the  next  step  was  to  hinge  it  to  one  of  the  contacts 
and  from  this  beginning  the  present  knife  switches  have  been 
developed. 

Underwriters  Rules. — The  rules  of  the  National  Board  of  Fire 
Underwriters  relative  to  knife  switches  state:  "All  switches  must 
have  ample  metal  for  stiffness  and  to  prevent  rise  in  temperature 
of  any  part  of  over  30  degrees  Centigrade  at  full  load,  the  con- 
tacts being  arranged  so  that  a  thoroughly  good  bearing  at  every 
point  is  obtained  with  contact  surfaces,  advised  for  pure  copper 

1 


SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


blades,  of  about  1  square  inch  for  each  75  amperes."  As  the 
result  of  many  tests  the  Underwriters  settled  on  certain  mini- 
mum spacings  between  points  of  opposite  polarity  for  various 
currents  and  voltages  of  250  D.C.  or  500  A.C.  and  for  600 
D.C.  Most  switches  are  designed  to  meet  these  requirements 
as  to  temperature  rise,  contact  surface,  spacing  and  other 
recommendations. 

Multiple  Blades. — Up  to  about  1200  amperes  in  capacity 
knife  switches  are  usually  made  with  single  blades,  while  for  larger 
capacity  two  or  more  blades  per  pole  are  supplied  in  order  to 
secure  sufficient  contact  surface  without  making  the  blades  and 
jaws  of  abnormal  width. 

Quick  Breaks. — "Auxiliary  breaks"  or  "quick  break  attach- 
ments" are  furnished  in  many  cases  so  as  to  make  it  impossible 
to  draw  a  dangerous  arc  by  opening  the  switch  slowly.  These 
quick  break  attachments  are  made  in  many  forms. 

Current-carrying  parts  of  a  well-designed  switch  consist  of  a 
high  grade  of  drawn  copper  of  guaranteed  conductivity.  The 
sectional  areas  and  contact  faces  of  all  sliding  and  stationary 
parts  are  calculated  in  accordance  with  the  best  practice,  and  a 
liberal  allowance  is  made  for  overloads. 

Temperature. — The  current-carrying  parts  adjacent  to  the 
contacts  will  carry  their  full-rated  current  continuously  with  a 
maximum  temperature  rise  of  either  20  or  30  degrees  Centigrade 
above  the  temperature  of  the  surrounding  atmosphere,  depend- 
ing on  the  class  of  service. 

The  rear  connected  switches  of  1200-ampere  capacity  and  larger 
are  given  a  lower  rating  for  alternating  current  than  for  direct 
current  and  are  not  guaranteed  to  carry  more  than  their  rated 
current. 


FIG.  1. — Typical  knife  switches. 

Momentary  Current. — The  maximum  momentary  current 
passing  through  knife  switches  should  not  be  greater,  owing  to 
mechanical  and  electrical  limitations,  than  50  times  their  normal 
60-cycle  20-degree  ampere  rating.  If  the  switches  will  be  sub- 


SWITCHES  3 

jected  to  greater  current  momentarily  than  this,  switches  of 
larger  normal  rating  (amperes)  should  be  used  as  they  are  both 
mechanically  and  electrically  stronger. 

Front  Connected. — Front  connected  knife  switches  are  listed 
by  most  makers  up  to  1200  amperes;  for  maximum  voltages  of 
250  volts  D.C.  or  A.C.,  500  volts  A.C.,  and  600  volts  D.C.  or 
A.C.;  with  and  without  quick  break  blades;  fused  and  unfused; 
single  and  double  throw. 

Rear  Connected  with  Round  Studs. — These  switches  are 
listed  in  capacities  up  to  1200  amperes  not  fused  and  600  amperes 
fused;  for  maximum  voltages  of  250  D.C.  or  A.C.,  500  A.C.  and 
600  D.C.  or  A.C.;  with  and  without  quick  break  blades;  single 
and  double  throw. 

Rear  Connected  with  Laminated  Studs. — These  switches  are 
furnished  with  the  conductor  slots  in  the  studs  horizontal,  or 
vertical  as  required.  They  are  listed  in  capacities  from  1600 
amperes  to  6000  amperes  for  250  volts  D.C.  and  500  volts  A.C., 
and  600  volts  D.C.  and  A.C.  without  fuses. 

Handles. — Spade  handles  are  regularly  furnished  on  all  4- 
pole  switches  and  on  all  3-pole  above  600-amperes  capacity; 
they  are  also  regularly  furnished  on  single  and  2-pole  switches 
with  laminated  studs.  All  other  knife  switches  have  straight 
handles. 

Fuses. — Fused  switches  are  arranged  for  National  Electrical 
Code  Standard  enclosed  fuses.  All  switches  that  are  fused  on 
the  hinge  jaws  have  high  jaws  to  allow  the  switch  handles  and 
blades  to  lie  fiat  on  the  fuses.  All  switches  that  are  fused  on 
break  jaws  have  high  break  jaws  to  allow  clearance  between 
handle  and  fuses. 

Switch  Studs. — The  smaller  capacity  switches  are  made  both 
rear  connected  and  front  connected,  while  the  larger  switches 
are  almost  invariably  made  rear  connection.  Up  to  approxi- 
mately 1200  amperes  the  standard  studs  for  rear  connected 
switches  are  circular  and  the  switch  studs  are  attached  to  their 
bases  by  nuts  screwed  on  these  circular  studs.  Additional  nuts 
are  provided  for  clamping  strap  connections  or  terminals.  For 
the  larger  capacity  switches  employed  on  low  voltage  boards, 
strap  connection  are  almost  invariably  used  and  to  facilitate  the 
employment  of  the  strap  connections  the  switch  studs  are  fre- 
quently made  laminated.  A  modification  of  the  laminated 
studs  made  with  copper  bars  employs  copper  studs  cast  under 


SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


high  pressure  by  means  of  which  the  conductivity  of  the  cast 
studs  is  approximately  90  per  cent,  that  of  rolled  copper. 
With  the  laminated  stud  switches  the  laminations  can  be  ar- 
ranged for  the  horizontal  or  vertical  plane  as  is  best  adapted  to 
the  wiring. 

Knife  Switches  for  A.C.  Service.— Up  to  800  amperes  there 
is  no  appreciable  difference  in  the  heating  of  knife  switches  on 
direct  current  or  alternating  current.  For  larger  capacities  it  is 
found  that  for  the  same  temperature  rise  it  is  necessary  to  derate 
the  larger  knife  switches  for  60-cycle  service.  The  constants 
vary  with  different  designs  and  different  capacities.  The  30- 
degree  rise  is  that  covered  by  the  Code  while  the  20-degree  rise 
is  the  one  that  is  desirable  for  hot  switchboard  rooms. 

Figure  1  shows  the  outlines  of  rear  connected  knife  switches  for 
D.C.  ratings  up  to  1200  amperes.  The  ratings  given  are  based 
on  D.C.  30-degree  rise  and  the  same  ratings  are  used  on  the 
switches  up  to  800  amperes  for  20  degrees  and  for  25-  and  60- 
cycle  service.  For  the  1200-ampere  size  the  30-degree  rating 
for  25  or  60  cycles  is  1100  amperes  while  for  20-degree  rise  the 
rating  is  1000  amperes  for  D.C.  or  A.C.  With  laminated  studs 
the  ratings  are  as  follows  for  the  larger  switches: 

MAXIMUM  AMPERES 


30  Degree  rating 

20  Degree  rating 

A  p 

A.C. 

D.C. 

D.C. 

25  Cycles 

60  Cycles 

25  Cycles 

60  Cycles 

1600 

1400 

1200 

1300 

1200 

1100 

2000 

1800 

1600 

1600 

1400 

1200 

3000 

2600 

2200 

2400 

2000 

1800 

4000 

3400 

2800 

3200 

2700 

2200 

6000 

4200 

3800 

4500 

3200 

2800 

Motor-starting  Knife  Switches. — Shown  in  Fig.  2  are  used  as 
a  simple  and  inexpensive  method  of  starting  synchronous  con- 
verters from  the  direct-current  end  and  direct-current  motors  of 
large  capacity  having  starting  conditions  that  will  permit  cutting 
out  the  starting  resistance  in  three  steps.  They  are  intended 


SWITCHES  5 

for  starting  conditions  only,  being  rated  in  terms  of  the  starting 
current,  and  a  short-circuiting  line  switch  or  circuit  breaker 
should  be  used  to  carry  the  running  load.  They  will,  however, 
carry  one-fourth  their  rated  current  continuously,  so  that  the 
short-circuiting  line  switch  can  be  omitted  where  the  full-load 
current  is  only  one-fourth  of  the  starting  current  rating  of 
the  switch. 


FIG.  2. —  Motor  starting  knife  switch. 

To  start  a  motor  the  switch  blade  is  thrown  into  the  first  jaw 
and,  after  a  moment's  pause  between  steps,  into  each  succeeding 
jaw  until  the  last  is  closed.  The  short-circuiting  line  switch, 
where  used,  is  then  thrown  in.  The  circuit  should  always  be 
opened  by  opening  the  line  switch  or  circuit  breaker. 

These  switches  have  four  sets  of  contacts  of  such  length  that 
the  switch  blade  makes  contact  with  each  set  in  succession. 
Each  switch  has  four  blades,  a  construction  that  allows  of  ample 
ventilation  and  reduces  the  depth  of  the  switch  from  the  switch- 
board. 

To  prevent  large  machines  being  started  too  quickly  by  throw- 
ing the  switch  through  all  the  positions  without  stopping  on  any 
one  position,  a  ratchet  device  is  provided  on  the  1200,  2400,  and 
3600-ampere  switches. 

Field-discharge  switches  are  used  in  the  field  circuits  of 
generators  to  serve  as  means  of  opening  and  closing  the  field 
circuit.  Just  before  the  knife  blades  of  the  switch  leave  the 


6  SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

contact  jaws,  an  auxiliary  blade  makes  contact  in  such  a  way 
tKat  the  discharge  resistor  is  connected  across  the  field  winding, 
thus  allowing  the  inductive  discharge  of  the  field  winding  to  die 
out  gradually . 

Field -transfer  switches  are  used  for  transferring  the  field  cir- 
cuits of  synchronous  converters  or  generators  from  one  source 
of  excitation  to  another  without  opening  the  supply  circuits, 
where  there  is  not  likely  to  be  a  difference  of  potential  between 
the  two  sources.  Where  such  a  difference  is  likely  to  occur,  a 
transfer  switch  with  additional  jaws  for  inserting  a  limiting  re- 
sistor between  the  supply  circuits  should  be  used.  They  are 
used  especially  where  it  is  necessary  to  transfer  a  synchronous 
converter  or  a  generator  field  circuit  from  the  bus  bars  to  the 
armature  for  self-excitation  or  to  a  direct-connected  exciter  as 
with  synchronous  converters  or  synchronous  motor-generator 
sets  started  from  the  direct-current  side. 

The  field-transfer  switches  are  operated  on  the  rocker  principle 
with  their  blades  so  shaped  that  just  before  one  side  leaves  the 
contact  jaws  the  other  makes  contact  with  its  jaws.  Thus  the 
field  circuit  is  not  opened.  The  single-pole  switches  are  used 
particularly  in  railway  service  using  grounded  return. 

The  remote-control  type  has  the  switch  mounted  on  a  sub-base 
in  the  rear  of  the  panel  and  connected  through  levers  to  an  oper- 
ating handle  mounted  with  a  cover  plate  on  the  switchboard 
panel.  The  operating  handle  has  a  latch,  by  means  of  which 
the  switch  may  be  locked  in  the  open  or  closed  position  at  the 
will  of  the  operator. 

The  safety -first  enclosed  knife  switch  is  used  in  steel  mills,  fac- 
tories, mines,  and  similar  places  employing  men  having  prac- 
tically no  knowledge  of  electricity  and  its  attendant  risks.  The 
danger  to  life  and  the  employer's  liability  for  death  or  injury  to 
a  man  touching  a  live  part  of  the  control  switch  or  to  a  repair- 
man inspecting  a  motor,  have  made  an  absolutely  safe  switch 
almost  a  necessity. 

The  safety-first  enclosed  knife  switch  case  contains  an  ordinary 
single-throw  knife  switch  with  enclosed  fuse  holders  at  the  hinged 
end.  These  are  mounted  in  an  exceptionally  strong  iron  box, 
certain  makes  having  a  partition  that  separates  the  switch 
blades  from  the  fuse  holders.  The  box  is  provided  for  conduit 
connections.  The  upper  or  switch  compartment  can  be  opened 
only  by  removing  two  machine  screws,  and  padlocks  when 


SWITCHES  7 

used;  it  is  necessary  to  open  this  compartment  only  when 
making  connections  and  in  case  of  inspection  or  repairs,  as  the 
switch  is  opened  and  closed  by  an  operating  handle  on  the  out- 
side of  the  box,  acting  through  a  shaft  and  lever  within.  The 
lower  or  fuse  compartment  contains  the  only  parts  that  need  be 
handled — fuses  to  be  replaced  when  blown  out.  The  door  of 
this  compartment  is  so  interlocked  with  the  switch  that  it 
can  be  opened  only  when  the  switch  is  in  the  open  position,  and 
with  this  door  opened,  the  switch  cannot  be  closed.  Conse- 
quently the  fuses  can  be  handled  only  when  disconnected  from 
the  live  line.  Due  to  the  partition,  it  is  impossible  to  reach  the 
live  parts  in  the  switch  compartment.  A  spring  is  sometimes 
provided  to  keep  the  door  of  this  compartment  closed.  The 
operating  handle  can  be  locked  with  the  switch  in  the  open 
position,  thus  preventing  tampering  by  unauthorized  persons 
and  protecting  repairmen  working  on  the  circuit. 

PLUG  SWITCHES 

Plug  switches  were  predecessors  of  the  knife  type  of  switch  but 
the  ordinary  plug  type  as  first  built  did  not  have  sufficient  spac- 
ing between  contacts  and  could  not  be  used  to  open  the  circuit 
under  load,  and  could  not  be  built  to  carry  more  than  200  or  300 
amperes  at  the  most,  so  that  the  design  of  the  knife  type  of 
switch  outstripped  the  plug.  For  certain  classes  of  service, 
however,  the  plug  switch  can  be  utilized  to  advantage.  Various 
types  of  plug  switches  have  been  developed  by  various  manu- 
facturers and  at  one  time  they  were  used  to  a  considerable  ex- 
tent for  A.C.  service  up  to  200  amperes  at  2400  volts  in  the  form 
of  "plunger  switches." 

In  the  single-pole  designs  plug-type  switches  are  still  used  to 
a  slight  extent  for  arc  lamp  service  and  similar  cases  where  a 
high  voltage  switch  of  small  current  capacity  rating  is  wanted. 
These  switches  consist  essentially  of  a  tube  of  fibre  or  similar 
material,  with  socket  contacts  at  each  end,  mounted  on  the  rear 
of  a  panel,  and  a  plug  consisting  of  a  metallic  rod  or  tube  with 
an  insulating  handle.  The  plug  when  inserted  through  a  hole 
in  the  switchboard  connects  together  the  contacts  at  each  end 
of  the  tube. 

Plug-type  instrument  switches  are  used  for  connecting  a  volt- 
meter, ammeter,  or  power  factor  meter  to  any  one  of  several 


8  SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

generators,  and  for  making  the  multi-point  connections  required 
when  synchronizing  generators. 

For  switchboard-voltmeter  circuits  the  receptacles  are  made  with 
2,  4,  6,  or  8  points.  The  metal  parts  are  recessed  in  a  bushing 
of  insulating  material  so  as  to  avoid  danger  of  accidental  short 
circuits.  The  separate  sockets  are  spaced  in  such  a  way  that 
the  plug  cannot  be  inserted  incorrectly,  it  thus  being  impossible 
to  short-circuit  the  line  through  the  plug. 

For  Portable-voltmeter  Circuits. — Receptacles  and  plugs  are 
used  for  connecting  a  portable  voltmeter  in  parallel  with  the 
switchboard  voltmeter  for  the  purpose  of  testing  the  accuracy  of 
the  latter.  A  lamp  cord  running  through  the  end  of  the  handle 
of  the  plug  connects  with  the  portable  instruments,  while  the 
receptacle  is  permanently  wired  up  to  the  switchboard  instrument. 

For  A.C.  Ammeter  Circuit. — Another  type  of  plug  is  used  for 
testing  the  switchboard  ammeter.  It  fits  the  same  receptacle 
and  is  identical  with  a  transfer  plug  except  that  it  has  a  lamp 
cord  which  makes  connection  through  the  handle  with  the  port- 
able ammeter.  This  plug,  when  inserted  in  the  receptacle,  con- 
nects the  portable  ammeter  in  series  with  the  switchboard 
ammeter,  in  the  current  transformer  secondary  circuit. 

By  the  use  of  transfer  plugs  and  receptacles,  one  ammeter  can 
be  used  to  indicate  the  current  in  each  phase.  The  primary  of 
a  current  transformer  is  connected  in  each  phase  of  the  circuit 
and  the  secondary  goes  to  the  line  terminals  of  its  receptacle 
where  it  is  normally  short-circuited.  When  the  plug  is  inserted 
in  a  receptacle  the  ammeter  is  connected  in  that  circuit. 

For  ground  detector  circuits  plugs  and  receptacles  are  used  with 
high  potential  push  buttons,  and  a  voltmeter  or  lamp  to  indi- 
cate the  existence  of  a  ground  on  1,  2,  or  3-phase  circuits.  For 
circuits  of  voltage  over  125,  switchboard  transformers  or  the 
necessary  lamps  in  series  are  required. 

Push-button  switches  are  sometimes  used  for  transformer  type 
ground  detectors,  engine-room  signals  and  similar  devices. 
These  are  frequently  arranged  as  the  equivalent  of  double-throw 
switches  normally  maintained  in  one  position  by  a  spring  to 
make  one  set  of  connections,  and  making  other  connections  when 
pushed  in  by  hand  or  some  of  the  switch  gear  mechanism. 

For  synchronizing  circuits,  plugs  and  receptacles  (Fig.  3)  are 
used  for  making  connections  to  synchronizing  instruments. 
Certain  types  have,  in  addition  to  the  contacts  for  making  the 


SWITCHES  9 

connections  to  the  synchronizing  instruments,  a  set  of  contacts 
of  40-amperes  capacity  through  which  the  control  circuit  of  the 
electrically  operated  generator  circuit  breaker  may  be  connected 
so  that  the  generators  can  be  thrown  on  the  bus  bars  only  when 
the  synchronizing  instruments  are  in  circuit. 


FIG.  3. — Synchronizing  plug  and  receptacle. 


DRUM  SWITCHES 

Drum-type  instrument  switches  are  used  for  connecting  one 
instrument  to  any  one  of  several  circuits  and  for  making  the 
multi-point  connections  required  when  synchronizing  generators. 

Construction. — Ruggedness  and  compactness  are  salient  fea- 
tures of  the  best  instrument  switches  in  a  typical  design.  Mov- 
able contact  members,  securely  mounted  on  a  substantial  bake- 
lite-micarta  drum,  engage  with  stamped  contact  fingers  as  the 
drum  is  rotated  to  the  right  or  left.  The  switching  element  is 
housed  in  a  substantial  bakelite-micarta  tube.  A  segment  of 
the  housing  is  easily  removable  for  inspection  and  adjustment. 

The  operating  key  is  of  black  moulded  material  with  a  polished 
black  finish;  the  dial-plate  markings  are  polished  copper,  on  the 
raised  parts,  with  a  black-mat  background;  and  the  housing  is 
finished  in  dull  black. 

All  of  these  instrument  switches,  with  the  exception  of  the 
ammeter  and  thermocouple  switches,  have  removable  keys  or 
handles.  These  keys  are  labeled  and  so  constructed  that  they 
cannot  be  inserted  in  the  wrong  switches. 

Ammeter  switch  is  so  made  that  with  one  ammeter,  one  am- 
meter switch  and  two  or  more  current  transformers  on  a  poly- 
phase circuit,  the  ammeter  can  be  connected  so  as  to  read  the 
current  in  any  phase.  Switching  contacts  are  so  arranged  that 
the  current  transformer  secondary  circuits  are  never  opened. 
For  connections  see  Fig.  4. 

Thermocouple  switch  is  built  so  that  with  one  switch  per  gen- 
erator, the  potentiometer  or  temperature  indicator  can  be  con- 


10          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


2  Phase  tmmeto  Snitch          3  Phase  tmneter  Switch 


fir-  1 1mpendent  Cir- 

famefer Switch  cult  tin '  meter  Switch 


*/«/ 


Onim  Detelipment 
Offftoitiea 


FIG.  4. — Ammeter  switch  connections. 


Circuit  Diagrams 


821  321 

Fio.  5. — Wattmeter  switch  connections. 


SWITCHES 


11 


nected  so  as  to  read  the  temperature  in  any  couple  or  search 
coil  on  any  machine. 

Voltmeter  switch  is  so  made  that  with  one  voltmeter  switch 
for  each  polyphase  circuit,  one  voltmeter  and,  for  service  above 
600  volts,  the  necessary  potential  transformers,  the  voltmeter 
can  be  connected  to  read  the  voltage  on  any  phase  of  any  circuit. 
One  key  is  required  for  each  voltmeter  and  its  group  of  switches. 
If  more  than  one  group  of  voltmeter  and  switches  is  desired, 
each  group  can  be  supplied  with  a  different  key  arrangement. 

Frequency-meter  switch  is  arranged  so  that  with  one  frequency 
meter  the  necessary  potential  transformers  and  one  switch  for 
each  bus  system,  the  frequency  can  be  read  on  any  bus  system. 
One  key  is  required  for  each  frequency  meter. 

Wattmeter,  watt-hour  meter,  power-factor  meter  and  reactive- 
factor  meter  switches  are  made  so  that  with  one  instrument,  one 
switch  with  proper  labeling  and  key  arrangement  for  each  single 
or  polyphase  circuit,  and  the  necessary  instrument  transformers, 
readings  can  be  taken  on  any  circuit.  One  key  is  required  for 
each  instrument.  For  connections  see  Fig.  5. 


TTp,"Tl" 


Note     This  ttjle  of  iirltch 

provided  with  two 

marked 

Ing  which  will  throw  the 

twitch  onlj  the 


Koto;  For  iTnohronlxIng  with  lamps  onlj  omit  : 

and  Insert  Individual  lamps  on  paneli  at  points  marked  x 

and  add  one  lamp  on  rear  of  board  u  ihown  bj  dotted  UDM 

FIG.  6. — Connections  for  synchronizing  between  machines. 

Synchronizing  switch  for  synchronizing  between  machines  is  so 
made  that  with  one  synchronoscope  equipment,  one  switch  for 
each  machine,  and  the  necessary  potential  transformers,  a  syn- 
chronizing indication  can  be  obtained  between  any  two  machines. 
One  running  key  and  one  incoming  key  are  required.  The  run- 


12          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


ning  key  is  to  be  placed  in  the  synchronizing  switch  of  one  of 
the  machines  running  and  can  be  turned  to  the  running  position 
only;  the  incoming  key  is  to  be  placed  in  the  synchronizing 
switch  of  the  machine  being  brought  in  and  can  be  turned  to 
the  incoming  position  only.  Each  switch  has  a  running  and  an 
incoming  position.  For  connections  see  Fig.  6. 

Synchronizing  switch  for  synchronizing  between  machine  and 
bus  is  so  made  that  with  one  synchronoscope  equipment,  one 
switch  for  each  generator  on  a  single-bus  system  and  two  switches 
for  each  generator  on  a  double-bus  system  and  the  necessary 
potential  transformers,  a  synchronizing  indication  between  the 
bus  and  any  incoming  machine  can  be  obtained.  One  key  only 
for  each  board  is  required.  Synchronizing  switches  are  built 
with  and  without  interlock  contacts  for  the  closing  circuit  of 
electrically  operated  circuit  breakers.  For  connections  see 
Fig.  7. 


Clrcuit  Diagram, 

For  Electrlodlj 
Operate  Breaker, 


««  i.?M>w  BfcrV       Puc  M«*-Opr.Bkn.or  Eta, 
Opr.Bte.Wlthou.tater.ock 


blDEle  Handle  Bjn. 

8w.»«  Etac  Opr.Bkrs. 

Poshfclu 


and  bus  .Ire  I  with  oonnectiuLS 
tkereto  Is  not  required. 
When  lamps  orjj  are  provided  bus 
win  I  trill,  connections  thereto 


FroinUcn.  }         From  ( 

FIG.  7. — Connections  for  synchronizing  to  bus. 


CONTROL  SWITCHES 

Control  switches  of  different  types  have  been  developed  for 
the  control  of  electrically  operated  devices  of  various  kinds,  put 
into  service,  and  then  superseded  by  later  devices. 

The  first  control  devices  were  small  single-pole,  double-throw 
knife  switches,  usually  made  with  a  spring  to  return  the  blade  to 
the  open  position  after  being  thrown  one  way  or  the  other.  A 
modification  of  this  switch  had  a  little  celluloid  plunger  located 
in  an  enlargement  of  the  blade,  colored  red  on  one  end,  green 


SWITCHES 


13 


on  the  other,  and  of  slightly  greater  length  than  the  depth  of 
the  blade.  The  color  of  the  end  that  was  projecting  from  the 
blade  showed  the  last  position  to  which  the  switch  had  been 
thrown. 

The  disadvantage  of  this  type  of  control  switch  was  the  possi- 
bility of  its  being  accidentally  operated  by  the  station  attendant 
when  reaching  for  another  device,  and  the  trouble  arising  from 
the  live  contacts  on  the  face  of  a  switchboard  where  there  were 
no  other  live  parts  on  the  front. 

G.  E.  Control  Switch. — A  push  button  for  closing  a  control 
circuit  and  another  for  tripping  was  an  early  scheme  adopted  to 
do  away  with  the  live  contacts  on  the  front.  The  push  button 
had  the  disadvantage  of  being  liable  to  accidental  closing  by  the 


FIG.  8. — General  Electric  Co.  pull  button  switch. 

switchboard  operator  so  a  "pull  button"  was  substituted  for  a 
push  button  and  the  twin  pull  button  shown  in  Fig.  8  has  been 
standardized  by  the  General  Electric  Company  for  control 
devices  on  switchboards. 

By  using  pull  buttons  in  place  of  push  buttons  there  is  little 
likelihood  of  the  attendant  operating  the  device  unintentionally 
when  cleaning  or  working  about  the  switchboard.  Red  and 
green  indicating  lamps  with  prismatic  lenses  are  used  for  signals 
and  a  little  target,  colored  red  and  green  and  located  between  the 
buttons,  shows  the  last  movement  that  has  been  made,  so  that  if 
the  target  shows  one  color  and  the  indicating  lamp  another  the 
breaker  has  tripped  automatically. 


14          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Lewis  and  Roth  combination  control  switch  and  indicating 
device  put  on  switchboards  made  by  them  embodies  the  essential 
features  of  no  live  parts  on  the  front  of  the  board,  a  position 
indicator  with  red  and  green  target,  the  usual  red  and  green 
indicating  lamps,  a  spring  return  to  the  off  position,  great 
compactness,  and  good  appearance  when  worked  into  a  miniature 
bus  arrangement. 

Westinghouse  Control  Switch. — The  Westinghouse  Electric 
&  Manufacturing  Company  first  tried  pull-button  switches  but 
soon  shifted  over  to  a  drum-control  switch  that  possessed  many 
features  that  it  was  difficult  to  embody  in  a  pull-button  device. 
By  varying  the  drum  development  and  the  number  of  contact 
fingers,  various  interlocks  could  be  made  and  one  control  switch 
could  handle  the  three  electrically  operated  breakers  for  motor 
starting,  the  forward  and  reverse  motion  with  limit  switches 
for  governors,  valves,  rheostats,  etc. 

Their  latest  control  switch  is  built  along  modern  and  latest 
practice  in  controller  design,  having  an  insulated  square  shaft 
for  carrying  the  moving  contact  segments  with  special  view  to 
securing  space  economy  while  having  due  regard  for  proper 
insulation,  as  shown  in  Fig.  9. 


FIG.  9. — Westinghouse  drum  control  switch. 

These  control  switches  have  been  designed  for  the  control  of 
circuits  governing  the  operation  of  solenoid  operated  switches 
and  circuit  breakers  or  their  control  relays,  solenoid  operated 
rheostats,  motor  operated  rheostats,  motor  operated  engine 
and  turbine  governors,  and  motor  operated  feeder-potential 
regulators. 

The  adaptability  of  the  control  switch  to  a  variety  of  special 
requirements  insures  a  neat  and  uniform  appearance  of  equipment 
on  the  front  of  the  switchboard.  As  an  aid  in  selection  for  the 
switchboard  operator,  control  switches  for  circuit  breakers  are 


SWITCHES  15 

provided  with  handles  of  a  different  shape  than  those  of  the 
other  control  switches. 

These  control  switches  will  successfully  handle  current  values 
of  considerable  magnitude.  However,  where  the  current  de- 
mands, of  closing  solenoids  in  particular,  are  in  excess  of  certain 
values,  a  control  relay  should  be  interposed  between  the  controller 
contacts  and  the  solenoid.  In  general,  control  relays  are  not 
usually  required  in  the  trip-coil  circuit  of  breakers. 

Construction. — Ruggedness  and  compactness  are  salient  fea- 
tures of  control  switches.  Advantage  has  been  taken  in  their 
design  of  the  years  of  successful  operation  and  experience  on 
railway  controller  contacts.  Rugged  stamped  contact  fingers 
of  the  same  type  as  employed  on  railway  controllers  are  used; 
the  advantages  of  the  horn-gap  construction  inherent  in  this 
design  are  well  known.  Movable  contact  members  mounted  on 
a  square  insulated  shaft  engage  with  stationary  spring-contact 
fingers  as  the  shaft  is  rotated  to  the  right  or  left.  The  switching 
element  is  housed  in  a  substantial  bakelite-micarta  tube,  which 
provides  a  simple  rigid  insulating  structure.  A  segment  of  the 
housing  is  easily  removable  for  inspection  and  adjustment. 

Space  Requirements. — The  switches  with  their  indicating 
lamps  can  be  mounted  3^  inches  between  vertical  center  lines 
and  7  inches  between  horizontal  center  lines,  or  7  inches  between 
vertical  center  lines  and  3)-^  inches  between  horizontal  center 
lines.  This  feature  is  in  keeping  with  modern  requirements  of 
space  economy  for  switchboards. 

Telltale. — All  control  switches  are  provided  with  a  mechani- 
cal indicating  device  that  shows  the  last  manual  operation  of  the 
control  switch.  When  the  handle  is  released,  the  switch  auto- 
matically returns  to  the  neutral  (central)  position. 

Lamp  Cut-out. — Several  designs  of  switches  for  the  control  of 
solenoid  operated  breakers,  embodying  a  signal  lamp  cut-out 
are  made.  The  oval  handle  on  these  switches  may  be  turned 
past  the  trip  position  to  a  lamp  cut-out  position  which  is  90 
degrees  from  the  neutral  (central)  position  and  there  latched  in 
place;  this,  therefore,  closes  the  circuit  to  trip  the  breaker,  and 
then  opens  both  the  trip  circuit  and  the  indicating  lamp  circuit 
with  the  breaker  "  locked  "  in  the  open  position.  On  double-bus  or 
relay-bus  systems,  this  permits  cutting  out  all  breakers  and  lamps 
on  the  bus  not  used;  the  horizontal  position  of  the  control  handles 
when  set  this  way  is  very  readily  observed  by  the  operator. 


16          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Lamp  indicators  are  connected  in  the  control  circuit  of  elec- 
trically operated  circuit  breakers  to  indicate  whether  the  breaker 
is  open  or  closed. 

Operation. — The  lamps  are  usually  so  connected  with  the  signal 
switch  on  the  breaker  that  when  the  breaker  is  closed  the  red 
indicator  will  be  lighted  and  when  the  breaker  is  open  the  green 
indicator  is  lighted.  On  one  style  of  the  control  switch,  an 
additional  indicator  is  so  connected  to  the  signal  and  control 
switches  that  when  the  breaker  is  tripped  automatically  this 
indicator  is  lighted  and  remains  lit  until  the  control  switch 
turns  to  the  "close"  or  "open"  position;  this  is  the  equivalent 
of  the  mechanical  indicating  device  that  is  self-contained  on 
certain  control  switches. 


FIG.  10. — Lamp  indicator. 

Construction. — Each  indicator,  shown  on  Fig.  10,  consists  of 
a  receptacle  projecting  through  the  switchboard  for  holding 
a  candelabra  lamp,  and  a  lens  holder  with  a  special  prismatic 
lens.  The  lamp  is  removable  from  the  front  of  the  panel  and 
the  receptacle  is  provided  with  a  glass-tube  fuse  at  the  back 
of  the  board.  The  lens  holder  is  pushed  into  the  end  of  the 
receptacle  from  the  front  of  the  board  and  is  held  firmly  by  spring 
clips.  A  special  feature  of  the  lens  is  the  prismatic  projection 
extending  across  its  face  which  makes  the  indications  visible 
from  any  position  in  front  of  the  board. 

These  indicators  are  arranged  for  mounting  on  2-inch  panels, 
but  can  be  used  on  l^-inch  and  13^-inch  boards  by  the  addition 
of  an  adapter. 

A  125  or  140-volt  candelabra  screw-base  lamp  should  be  used. 
For  control  voltages  over  140,  the  140-volt  lamp  should  be  used 
with  suitable  resistor. 

Control  Relays. — Control  relays  are  interposed  between  the 
contacts  of  a  main  relay  or  the  contacts  of  a  control  switch  and 
the  apparatus  to  be  controlled,  when  the  current  required  to 


SWITCHES  17 

operate  the  apparatus  exceeds  the  current-carrying  or  interrupt- 
ing capacity  of  the  main  relay  or  control  switch  contacts. 

Control  relays  are  thus  frequently  required  for  the  closing-coil 
circuits  of  electrically  operated  carbon  and  oil  circuit  breakers. 
In  general,  the  tripping-coil  circuits  of  circuit  breakers  do  not 
require  sufficient  current  to  make  necessary  the  use  of  control 
relays. 

Operation. — The  operating  coil  for  the  control  relay  is  connec- 
ted directly  across  the  control  circuit  by  the  closing  of  the  control 
switch,  causing  the  control  relay  to  close,  connecting  the  circuit- 
breaker  closing  coil  across  the  line. 

Control  relays  are  given  a  maximum  current  and  voltage 
rating  based  on  intermittent  operation.  They  will  give  satis- 
factory service  for  intermittent  duty,  namely,  with  power  im- 
pressed thereon  for  not  more  than  10  seconds  out  of  every  60; 
this  is  the  condition  found  under  usual  operating  requirements. 

Construction. — These  control  relays  are  an  adaptation  of  the 
well  known  "contactor  type"  of  switch  used  most  extensively 
for  industrial  motor  control. 

The  contacts,  which  have  ample  overload  capacity,  are 
pressed  firmly  together  with  a  self-cleaning  action. 

Flexible  copper  shunts  carry  the  current  from  the  moving 
contact  to  the  lower  terminal  of  the  relay.  No  current  passes 
through  pins,  springs,  or  bearing  surfaces.  The  top  contact  is 
stationary  and,  therefore,  requires  no  shunt. 

Blowout  coils  are  used  on  all  switches.  The  blowout  coils 
and  arcing  horns  are  very  efficient  in  operation,  the  blowout 
coils  being  of  special  design  to  handle  the  highly  inductive  control 
circuit.  The  arc  is  distributed  over  a  relatively  large  area  as 
soon  as  formed  and  is  quickly  extinguished.  Hence  it  has 
practically  no  destructive  action. 

DISCONNECTING  SWITCHES 

Knife-type  disconnecting  switches  are  used  for  isolating  oil 
circuit  breakers,  feeders,  etc.,  or  for  making  various  connections 
that  do  not  have  to  be  opened  under  load. 

In  American  practice  the  knife  switches  for  2500  volts  or  less 
are  usually  mounted  directly  on  a  base  of  soapstone,  marble  or 
similar  material,  while  for  higher  voltages,  insulators  of  various 
kinds  are  used  to  support  the  switch  jaws.  Up  to  2500  volts 
these  disconnecting  switches  are  made  either  front  connection, 


18 


SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


FIG. 


11.  —  Heavy    duty    disconnecting 
switch. 


or  rear  connection,  or  both,  while  for  higher  voltages  than  25,000 
they  are  almost  invariably  made  front  connection  only. 

For  light  service,  switches  with  petticoat  insulators  are  em- 
ployed, these  being  made  for 
inverted  mounting  or  for 
vertical  mounting. 

For  heavy  duty,  Fig.  11 
shows  a  4000-ampere,  15,000- 
volt  disconnecting  switch. 
This  type  is  built  in  capacities 
of  400  up  to  4000  amperes  at 
7500  and  15,000  volts,  and  up 
to  600  amperes  for  higher 
voltages  up  to  and  including 
73,000.  In  this  switch  a 
corrugated  conical  pillar  type 
insulator  is  used  with  the 
switch  part  attached  to  the 
top  of  the  insulator  and  the 
bottom  of  the  insulator  at- 
tached to  a  metal  base  in 

such  a  manner  that,  if  an  insulator  proves  defective,  it  can 
readily  be  replaced  without  the  necessity  of  replacing  the  bal- 
ance of  the  switch.  Owing  to  the  severe  mechanical  stresses 
set  up  at  the  instant  of  short  circuit  on  systems  of  large 
capacity,  latches  are 
provided  on  these  dis- 
connecting switches  to 
prevent  them  being 
blown  open. 

For  voltages  of  73,000 
and  above,  it  is  cus- 
tomary to  employ  dis- 
connecting switches  like 
Fig.  12,  mounted  on 
porcelain  posts  of  the 
built-up  type  employing 
a  sufficient  number  of 

sections  or  units  to  secure  the  voltage  test  desired,  either  for 
indoor  or  for  outdoor  service. 

With  this  type  of  switch,  if  an  insulator  becomes  damaged  or 


FIG.  12. — Disconnecting  switch  with  built  up 
insulator  column. 


SWITCHES 


19 


defective,  the  units  can  be  readily  unbolted  from  the  built-up 
pillar  and  replaced  by  a  new  section. 

Fig.  13  shows  a  series  of  switches  made  for  voltages  from 
22,000  to  110,000.  These  are  mounted  on  corrugated  pillar  type 
insulators  that  are  given  a  dry  test  of  three  times  normal  voltage. 
On  the  larger  sizes  a  truss  blade  is  furnished  to  secure  rigid  con- 
struction and  safety  catches  are  supplied  to  prevent  the  switches 
jarring  open.  The  caps  holding  the  jaw  blades  are  clamped  to 
a  wall  or  other  flat  structure  after  they  are  removed  from  the 
wooden  template  on  which  the  switches  are  shipped. 

The  Delta-Star  Electric  Company  have  the  blades  of  their 
disconnecting  switches  made  either  plain,  for  normal  light  ser- 
vice, or  with  latches  of  various  types  where  the  short-circuit 


FIG.  13. — Line  of  General  Electric  Co.  disconnecting  switches. 

current  is  such  that  there  is  a  possibility  of  the  magnetic  stress- 
es blowing  the  switch  open  if  it  were  not  provided  with  latches. 

A  very  compact  type  of  disconnecting  switch  for  attaching 
to  a  bus  bar  is  shown  in  Fig.  14.  In  place  of  cable  terminal  at 
the  hinge  jaw  of  switch,  provision  can  be  made  for  copper  strap 
connection. 

All  of  the  disconnecting  switches  previously  described 
have  been  single  pole  and  are  operated  by  means  of  a  hook  stick. 
The  various  companies  make  modifications  for  multipole  service 
mechanically  operated  as  shown  in  Fig.  15  this  being  a  Delta- 
Star,  three-pole  double-throw  distant-control  switch.  Any 
combination,  front  or  rear  connected,  can  be  supplied. 

Outdoor  high  voltage  disconnecting  switches  of  one  design  are 
built  with  each  pole  mounted  on  three  insulators,  the  end  ones 


20          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

carrying  break  jaws  and  the  line  connectors  being  stationary, 
the  middle  one  carrying  the  switch  blade  rotating  in  such  a  way 
as  to  introduce  a  double  break  into  the  line. 


FIG.  14.  FIG.  15. 

FIG.  14. — Delta-Star  bus-bar  switch. 

FIG.  15» — Outdoor  high  voltage  3  P.  D.  T.  distant  control  disconnecting 
switch. 


HORN -BREAK  SWITCHES 

Where  it  is  necessary  to  open  up  a  high  tension  outdoor  line 
with  power  on  or  when  supplying  the  charging  current  for  a  long 
transmission  line,  it  is  necessary  to  provide  arcing  horns  for  the 
switches,  if  oil  breakers  are  not  employed.  These  horn-break 
switches  have  been  made  by  various  builders. 

Fig.  16  shows  a  50-K.V.  horn-gap  switch  made  in  single-pole 
units  but  arranged  so  that  any  number  of  poles  can  be  mechanic- 
ally interconnected  by  means  of  an  adjustable  bar  and  operated 
from  a  single  operating  handle.  The  main  contacts  are  protected 
from  all  burning  by  the  auxiliary  arcing  horns  which  make  con- 
tact before  the  main  contact  is  closed,  and  which  break  away 
after  the  main  contact  is  opened.  The  main  contact  itself  is 
completely  covered  by  a  sleet  hood  and  protected  from  burning 
by  the  auxiliary  arcing  horn. 


SWITCHES 


21 


FIG.  16. — R.  &  I.  E.  Co.  horn-gap  switch  50-K.V.  single  break. 


END    VIEW 

Fia.  17. — Horn-gap  switch  70-K.V.  double  break. 


22          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

For  70-K.V.  service  these  switches  as  shown  in  Fig.  17  are 
made  double  break  in  order  to  obtain  the  proper  gaps  in  the  line. 
These  switches  are  intended  primarily  for  mounting  on  a  pole 
top  or  a  structure  with  the  insulators  in  the  vertical  position 
and  the  switch  arm  swinging  around  on  a  horizontal  plane. 


FIG.  18.— R.  &  I.  E.  Co.  horn-gap  switch  120-K.V.  vertical  break. 

For  still  higher  voltages  a  switch  of  the  type  shown  in  Fig.  18 
is  utilized.  This  switch  is  designed  for  120-K.V.  service,  and 
while  the  porcelain  pillars  are  mounted  in  a  vertical  position,  the 
switch  arm  is  so  arranged  as  to  swing  open  in  a  vertical  plane 
instead  of  a  horizontal  one. 

Where  it  is  desired  to  obtain  automatic  protection  for  a  sub- 
station or  sectionalizing  of  a  line  at  a  moderate  cost,  an  automatic 
attachment  can  be  added  to  these  horn-gap  switches. 

The  insulator  which  carries  the  solenoid  trip  is  mounted  in  a 
bearing,  and  is  capable  of  rotation  through  a  small  angle  under 
the  torsion  of  a  spring.  The  trip  coil  is  energized  by  the  main 


SWITCHES  23 

line  current.  On  overload,  the  plunger  in  the  trip  coil  magnet 
releases  the  latch  allowing  the  insulator  to  swing  by  force  of  the 
spring.  This  motion  moves  a  trip  rod  which  releases  a  main 
latch,  allowing  the  3  poles  of  the  switch  to  open  simultaneously. 
The  switch  automatically  resets  by  bringing  the  operating  handle 
to  the  open  position.  The  switch  cannot  be  held  closed  on  an 
overload,  or  on  a  short  circuit. 

Modification  of  this  series  trip  mechanism  can  be  applied  to 
the  double-break  or  the  vertical-break  horn-type  switch. 


CHAPTER  II 

AUTOMATIC  PROTECTION  AND  FUSES 
GENERAL  FEATURES 

One  of  the  most  important  features  of  switch  gear  is  the 
automatic  protection  secured  by  means  of  fuses,  circuit  breakers 
or  similar  devices  which  guard  the  various  circuits  against  the 
trouble  that  may  arise  from  overloads  or  any  other  condition 
apt  to  cause  damage. 

A  constant  potential  generator  tends  to  maintain  its  voltage 
independent  of  the  amount  of  current  it  may  be  developing. 
With  a  B.C.  generator,  unless  this  current  is  limited  by  some 
automatic  device,  the  excessive  current  is  very  apt  to  damage  the 
armature  and  particularly  the  commutator,  so  automatic  pro- 
tection is  usually  furnished  to  prevent  the  current  in  a  D.C. 
generator  reaching  a  value  apt  to  damage  it. 

Exciter  and  Field  Circuits. — It  has  become  standard  practice, 
however,  not  to  supply  automatic  protection,  such  as  fuses  or 
circuit  breakers,  in  exciter  and  field  circuits,  as  the  sudden  open- 
ing of  the  field  circuits  of  the  A.C.  generators,  due  to  the  operation 
of  a  fuse  or  breaker  in  the  field  or  exciter  circuit,  might  cause 
far  greater  damage  due  to  puncturing  the  insulation  of  the  A.C. 
generator  than  would  arise  from  the  overloading  or  even  short- 
circuiting  of  an  exciter.  In  some  cases  fuses  are  furnished  in 
exciter  circuits  of  two  or  three  times  the  normal  capacity  of  the 
machine  so  that  no  ordinary  overload  could  cause  them  to  blow 
while  a  certain  amount  of  protection  will  be  afforded  to  the  exciter 
against  a  dead  short  circuit. 

Where  the  exciters  also  supply  current  for  station  service 
automatic  protection  is  sometimes  supplied  that  will  cut  off  the 
station  circuits  in  case  of  trouble  while  leaving  the  exciter  con- 
nected to  the  field  bus.  Where  exciters  are  used  in  parallel 
with  a  battery  and  in  certain  other  conditions,  reverse-current 
circuit  breakers  are  supplied  in  the  exciter  circuit  that  will  open 
only  when  the  exciter  tends  to  draw  power  from  the  bus  bars 
instead  of  delivering  power  to  them. 

24 


AUTOMATIC  PROTECTION  AND  FUSES  25 

A.C.  Generators. — With  the  exception  of  some  generator  panels 
where  fuses  or  breakers  are  furnished  for  the  protection  of  a  line 
fed  directly  from  the  machine  or  of  feeders  run  from  the  A.C. 
bus  bars  without  other  protection,  it  is  customary  to  omit  any 
fuses,  circuit  breakers,  or  other  automatic  devices  in  the  armature 
circuits  of  the  A.C.  generators  as  most  machines  have  sufficient 
armature  reaction  to  enable  them  to  stand  short  circuits  for  a 
short  time  without  damage  to  themselves.  In  other  words,  no 
protection  is  needed  for  a  moderate  size  A.C.  generator  with 
fairly  high  armature  reaction. 

With  some  very  large  machines  of  low  armature  reaction  or 
important  installations  it  is  sometimes  advisable  to  use  a  circuit 
breaker  in  the  generator  circuit  with  a  reverse-current  time  limit 
relay,  but  such  cases  are  usually  special  and  form  an  exception  to 
the  general  rule. 

Differential  Protection. — More  recently  a  scheme  of  differential 
protection  for  large  generators  has  become  almost  universal, 
utilizing  current  transformers  in  each  end  of  each  phase  winding 
of  a  generator,  i.e.,  at  the  neutral  as  well  as  in  the  outgoing  leads 
and  balancing  these  against  each  other.  For  all  conditions  of 
overload  or  external  short  circuit  the  system  is  non-automatic, 
but  any  internal  short  circuit  or  ground  in  the  generator  will 
cause  an  unbalancing  in  the  relay  circuit  causing  the  tripping  of 
the  generator  breaker  and  field  switch. 

Converters. — For  the  protection  of  synchronous  converters 
or  motor-generator  sets,  the  rules  applied  to  D.C.  generators 
apply  for  the  direct-current  end  of  the  machine.  The  circuit 
breaker,  which  is  almost  invariably  used  in  the  D.C.  circuit,  is 
usually  provided  with  a  low  voltage  release  coil  in  addition  to 
the  usual  overload  coil,  and  this  release  coil  may  be  short- 
circuited  by  a  reverse-current  relay  if  it  is  desired  to  guard  against 
the  machine  taking  in  D.C.  current  and  delivering  A.C.  current. 
The  speed  limit  device,  when  furnished,  usually  short-circuits 
this  low  voltage  release  coil  to  cut  off  the  D.C.  current  in  case 
of  excessive  speed. 

For  the  A.C.  end  of  a  converter  fed  directly  from  a  low  tension 
generator  or  bus,  automatic  protection  is  usually  furnished. 
When  fed  from  its  own  transformer  or  bank  of  transformers,  the 
automatic  protection  is  usually  supplied  on  the  high  tension  side 
of  the  transformers  and  no  automatic  devices  are  used  between 
the  A.C.  end  of  the  converter  and  the  low  tension  transformer 
circuit. 


26         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Circuit  Protection. — In  a  generating  station  with  A.C.  genera- 
tors supplying  power  to  a  low  tension  bus,  which  in  turn  fur- 
nishes current  to  step  up  transformers  feeding  a  high  tension  bus 
and  outgoing  transmission  lines,  it  is  customary  as  previously 
explained  to  make  the  generator  breakers  non-automatic.  Those 
for  the  low  tension  side  of  the  transformers  are  made  overload 
automatic,  those  for  the  high  tension  side  of  the  transformers 
non-automatic,  those  for  the  outgoing  lines  automatic  and  any 
tie  or  junction  breakers  in  the  bus  bars  non-automatic.  In  a 
step  down  transformer  station  the  same  scheme  is  followed 
except  that  the  high  tension  transformer  breaker  is  automatic 
and  the  low  tension  non-automatic.  Occasionally  with  trans- 
formers differential  relay  devices  are  used,  operated  from  current 
transformers  in  the  high  tension  and  low  tension  circuit  in  such 
a  manner  that  as  long  as  the  ratio  of  transformation  remained 
practically  constant,  the  breakers  would  be  non-automatic  but 
if  any  internal  trouble  in  the  transformer  modified  this  ratio  of 
transformation,  the  differential  relay  would  act  and  both  high 
tension  and  low  tension  breakers  would  be  tripped  out. 

FUSES 

Fuses,  open  link,  at  first  were  small  copper  wires  and  their 
great  drawback  was  the  high  melting  point  of  the  copper  and 
the  consequent  heat  of  the  molten  metal  dropping  from  the 
fuse  and  the  formation  of  copper  globules.  To  reduce  the 
heat  of  the  molten  metal,  lead,  tin,  or  some  alloy  with  low  fusing 
point  was  used,  but  such  fuses  had  the  drawback  of  being  too  soft 
and  easily  damaged  when  tightening  up  the  contact  nuts.  The 
next  step  was  to  use  alloy  fuses  with  copper  tips  and  these  are 
still  used  to  some  extent. 

As  the  price  of  aluminum  was  reduced  this  material  was  used 
largely  for  fuses  as  it  has  a  high  conductivity  reducing  the 
amount  of  metal  fused,  a  fairly  low  melting  point  and  almost 
complete  vaporization  of  the  metal  fused.  By  using  wide  strips 
of  aluminum  cut  to  form  two  or  more  bridges,  fairly  reliable  open 
fuses  can  be  made  up  to  1200  amperes.  An  ordinary  metal 
strip  exposed  to  draughts  of  various  kinds  is  apt  to  be  very  erratic 
in  its  behavior  as  a  fuse  and  is  apt  to  throw  molten  metal  when  it 
blows.  These  defects  in  the  behavior  of  open  fuses  finally 
led  to  various  devices  to  remedy  these  troubles — one  being  the 
enclosure  of  the  fuse  in  a  suitable  receptacle  or  tube. 


AUTOMATIC  PROTECTION  AND  FUSES 


27 


FIG. 


19. — Typical   expulsion    fuse    and 
block. 


Fuses,  Expulsion. — It  was  found  that  the  fuses  for  1100-and 
2200-volt  service  were  decidedly  dangerous  unless  properly 
covered  up,  and  if  they  were  placed  in  an  airtight  box  they  were 
apt  to  rupture  the  box  by  the  explosion  of  the  gases  formed  when 
the  fuses  blew.  It,  therefore,  became  necessary  to  provide  a  vent 
for  the  gases  and  the  natural  development  was  to  place  the  vent 
in  such  a  position  that  the  gases  in  expanding  caused  a  strong 
draught  through  the  vent  and 
this  was  used  for  blowing  out 
the  arc.  This  resulted  in  the 
expulsion  type  of  fuse  holders. 

The  earliest  designs  of  this 
type  comprised  a  removable 
fuse  holder  of  lignum  vitae 
or  similar  tough  close-grained 
wood,  equipped  with  termi- 
nals which  fit  into  suitable 
blocks.  Later  types  have  the  fuse  placed  in  a  fibre  tube  and 
arranged  to  blow  out  through  one  end  like  a  bomb. 

Fig.  19  shows  a  typical  expulsion  type  fuse  block  for  indoor 
service"  up  to  7500  volts  in  capacities  up  to  100  amperes  and  simi- 
lar fuse  holders  are  available  up  to  25,000  volts. 

These  fuse  blocks  are  made  especially  for  opening  the  circuit 
in  the  event  of  sudden  and  severe  overloads  or  short  circuits, 
but  they  are  also  entirely  suitable  for  the  protection  of  circuits 
in  the  case  of  gradually  increasing  overloads  if  the  fuse  wire  is 
inserted  in  asbestos  sleeving. 

The  fuse  tube  is  readily  removable  from  the  contact  clips 
and  the  fuse  wire  easily  inserted  therein,  making  the  re-fusing 
a  very  simple  matter.  These  fuse  blocks  will  operate  satisfactor- 
ily on  any  circuits  within  their  interrupting  capacity,  which  is 
approximately  1000  amperes  at  7500  volts  when  used  one  per 
wire  and  proportionately  greater  or  less  at  other  lower  or  higher 
voltages. 

The  fuse  tube  is  hollow  and  one  end  is  left  open,  so  that  when 
the  fuse  blows,  the  metallic  vapors  are  expelled  from  the  tube 
through  the  open  end  and  successfully  extinguish  any  arc  inci- 
dent to  the  blowing  of  the  fuse.  Before  being  inserted  in  the  fuse 
tube  the  fuse  wire  should  be  enclosed  in  asbestos  sleeving.  The 
asbestos  sleeving  prevents  the  gradual  charring  of  the  inside  of 
the  fuse  tube  by  the  overheated  fuse  and  thereby  eventually 


28          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

lengthens  the  life  or  prevents  burning  out  of  the  fuse  tube.  The 
open  end  of  the  fuse  tube  extends  beyond  the  contact  jaw  so  that 
all  danger  of  the  expelled  vapors  coming  in  contact  with  the 
metallic  portion  of  the  block  is  eliminated. 

Enclosed  fuse  consists  essentially  of  a  fusible  wire,  strip  or 
sets  of  wires  and  strips  enclosed  within  a  tube,  usually  of  fibre, 
filled  with  a  material  to  exclude  the  air  and  to  facilitate  the 
opening  of  the  circuit  when  the  fuse  blows  by  absorbing  the  gases 
formed  and  chilling  out  the  arc.  Suitable  terminals  are  provided 
so  that  the  fuse  may  be  mounted  in  a  fuse  block. 

N.E.C.  Fuses. — When  enclosed  fuses  were  first  put  on  the 
market  each  manufacturer  developed  his  own  designs  of  terminals 
and  used  his  own  spacings  so  that  there  was  no  uniformity 


D IPO 


FIG.  20. — Enclosed  fuse  with  ferrule  FIG.  21. — Enclosed    fuse    with    blade 

contacts.  contacts. 

and  the  fuse  of  one  make  could  not  be  used  in  the  fuse  holder  of 
another  manufacturer.  To  avoid  this  confusion  the  representa- 
tives of  the  fuse  builders  and  the  National  Board  of  Fire  Under- 
writers finally  adopted  certain  standard  dimensions  and  types 
of  contacts  for  various  sizes  and  voltages.  Up  to  60  amperes 
ferrule  type  contacts  are  used  as  shown  in  Fig.  20,  and  from  61 
amperes  to  600,  knife  blade  contacts  are  employed  as  shown  in 
Fig.  21.  One  set  of  dimensions  are  used  for  fuses  up  to  250  volts 
and  another  for  fuses  up  to  600  volts.  Fuses  that  correspond 
to  the  accepted  dimensions  and  that  meet  other  requirements 
agreed  on  are  known  as  National  Electrical  Code  (N.E.C.) 
fuses  and  are  perfectly  interchangeable. 

Limits. — On  large  systems  the  circuit  characteristics  should  be 
such  as  to  limit  the  maximum  overload  power  passing  through 
the  fuse  to  approximately  10,000  kilo  volt-amperes.  Circuit 
breakers  are  recommended  instead  of  enclosed  fuses  where  the 
rated  capacity  of  the  generators  supplying  the  circuit  on  which 
they  are  directly  installed  exceeds  2000  kilovolt-amperes,  as  fuses 
are  not  suitable  for  such  circuits. 

Indicators. — Each  fuse  is  provided  with  a  simple  but  reliable 
device  which  indicates  whether  the  fuse  has  blown  or  is  still 


AUTOMATIC  PROTECTION  AND  FUSES  29 

intact.     This  indicator  is  in  plain  view  so  that  the  condition  of 
the  fuse  can  be  determined  at  a  glance. 

Fuse  blocks  and  fuse  holders  for  enclosed  cartridge  fuses  for 
voltages  up  to  25,000,  front  and  rear  connected,  are  used  for 
mounting  on  the  wall  or  on  switchboard  panels  and  are  rated 
according  to  the  ampere  and  voltage  capacities  of  standard 
cartridge  fuses  with  which  they  are  designed  to  be  used,  and  the 
ratings  apply  to  either  direct  or  alternating  current. 

The  250-volt  and  600-volt  fuse  blocks  have  the  National  Elec- 
trical Code  standard  dimensions  and  will  receive  any  cartridge 
fuses  of  corresponding  ampere  capacities  conforming  thereto. 

Fuse  blocks  for  glass  cartridge  fuses  for  capacities  up  to 
2  amperes,  250  volts,  single,  two  and  three-pole  use  a  small 
glass-tube  fuse  of  2-amperes  capacity.  They  are  used  princi- 
pally for  the  protection  of  instruments  connected  directly  to  the 
line  without  transformers  and  in  the  secondary  circuit  of  in- 
strument transformers. 

The  complete  block  consists  of  fuse  clips  of  the  ferrule  type 
mounted  on  porcelain  blocks  with  barriers  on  the  outside  edges 
and,  with  the  two  and  three-pole  blocks,  between  poles.  They 
are  made  for  mounting  on  the  wall  or  in 
the  rear  of  panels  and  are  front  connected. 

Switchboard-type  fuse  blocks  as  shown  in 
Fig.  22  are  made  for  switchboard  use 
where  it  is  desired  to  replace  the  fuse 
from  the  front  of  the  panel.  The  standard 
enclosed  fuse  is  inserted  in  the  clip  in  the 
plug  and  the  plug  is  then  screwed  into  the 
receptacle  until  the  fuse  enters  the  inner  contacts.  These  fuse 
blocks  are  for  1^-inch,  1^-inch  and  2-inch  panels. 

Fuse  blocks  with  porcelain  insulators  and  cast-iron  or  sheet- 
steel  bases,  wall  mounting  type,  are  used  for  the  protection  of 
switchboard  mounting  and  other  voltage  transformers  of  small 
capacity  for  voltages  up  to  25,000  maximum.  They  can,  how- 
ever, be  used  on  any  circuit  up  to  their  rated  capacity. 

Transformer  Fuses. — When  the  A.C.  system  was  developed 
with  distributing  transformers  mounted  on  houses  or  poles  and 
exposed  to  the  weather,  it  became  necessary  to  develop  suitable 
fuse  protection  for  them  and  various  types  of  fuse  blocks  and 
fuse  holders  were  designed.  The  usual  form  for  moderate 
capacity  transformers  on  7500-volt  circuits  was  a  porcelain  fuse 


30 


SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


holder  carrying  a  small  piece  of  fuse  wire  placed  in  deeply  re- 
cessed grooves  in  the  fuse  holder  but  as  voltages  increased,  it 
became  necessary  to  go  to  another  type. 

Fig.  23  shows  a  25,000-volt  combination  fuse  holder  and  dis- 
connecting switch  developed  for  outdoor  service  and  this  fuse 
holder,  of  the  expulsion  type,  can  readily  be  made  suitable  for 
higher  voltages  by  using  larger  insulators  and  increasing  the 
dimensions  of  the  fuse  tube. 


FIG.  23. — Disconnecting  switch  type  of  expulsion  fuse. 

S.  &  C.  Fuse. — Another  type  of  fuse,  known  as  "The  S.  &  C. 
Fuse"  but  sometimes  called  "Carbon  Tetrachloride  Fuse"  has 
been  developed  by  Schweitzer  &  Conrad,  Inc.  These  have  been 
used  outdoors  and  indoors  for  voltages  up  to  115,000  and  in 
current  capacities  up  to  400  amperes.  The  fuse  is  located  in  a 
glass  tube  that  contains  a  spiral  spring,  the  lower  end  of  which  is 
connected  to  the  bottom  ferrule.  The  upper  end  of  the  spring 
connects  to  the  fuse  wire  passing  through  a  cork,  the  upper  end 
of  the  fuse  wire  being  connected  to  a  short  wire  soldered  to  the 
cap  on  the  top  ferrule.  At  the  top  of  the  spiral  spring  and  just 
below  the  cork  is  a  funnel-shaped  liquid  director.  The  glass  tube 
is  filled  with  a  noninflammable  liquid  of  extremely  high  dielectric 


AUTOMATIC  PROTECTION  AND  FUSES 


31 


strength,  having  none  of  the  objectionable  characteristics  of  oil. 
This  liquid  is  not  only  not  an  oil,  and  therefore  noninflammable, 
but  is  one  of  the  most  effective  fire  extinguishing  liquids  known. 

Operation. — The  melting  of  the  fuse  wire  releases  the  spiral 
spring  which  contracts  instantaneously,  drawing  the  fuse  wire 
down  towards  the  bottom  of  the  tube  and  thus  introducing  a  very 
large  gap.  Simultaneously  with  the  introduction  of  this  gap,  the 
liquid  extinguishes  the  arc  and  interrupts  the  current  flow,  the 
rapidity  of  its  action  being  accelerated  by  the  liquid  director  which 
is  drawn  down  with  the  spring  and  so  forces  the  liquid  directly 
on  to  the  moving  terminal. 

Since  the  dielectric  strength  of  the  liquid  is  about  250,000  volts 
per  inch,  the  gap  between  the  top  ferrule  and  the  top  end  of  the 
submerged  spring  gives  an  enormous 
factor  of  safety.  The  dimensions  of 
the  glass  tube  and  other  parts  vary, 
depending  upon  the  ampere  capacity 
and  voltage  rating  of  the  fuse.  Ac- 
cording to  tests,  this  fuse  operated  in 
less  than  one-fifth  of  the  time  required 
by  oil  circuit -breakers;  the  longest 
time  required  to  open  the  circuit  was 
0.03  seconds.  This  is  remarkable 
when  compared  to  the  quickest  oper- 
ating oil  circuit  breaker  which  takes 
at  least  4  cycles  on  25-cycle  current, 
or  a  minimum  of  0.16  seconds. 

Weatherproof  Cut-out. — For  use  as 
a  weatherproof  primary  cut-out,  a 
special  holder  of  moulded  insulating 
material  is  provided.  The  S.  &  C. 
Fuse  attached  to  a  handle  of  the  same 
material  as  the  holder,  fits  into  the 
holder  in  such  a  manner  as  to  make 
a  bayonet  type  plug  switch. 

Fused  Switch. — The  fused  switch  is  furnished  for  those  installa- 
tions where  it  is  desired  to  install  a  combination  disconnecting 
switch  and  fuse  mounting,  but  where  the  space  is  so  limited  that 
the  regular  types  cannot  be  used. 

The  middle  portion  of  the  disconnecting  blade  is  replaced  by 
two  pieces  of  Bakelized  insulating  material,  and  the  fuse  is 


Fro.  24. — Schweitzer-Conrad 
shunted  switch  with  carbon 
tetra-chloride  fuse. 


32 


SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


mounted  across  this  insulated  gap  so  that  the  current  is  carried 
through  the  fuse.  The  fuse  is  mounted  in  regular  fuse  clips 
with  the  regular  retaining  bales,  so  that  no  difficulty  is  en- 
countered in  the  opening  and  closing  of  the  blade. 

Shunted  Switch  (Fig.  24) . — Another  adaptation  of  this  type  of 
fuse  consists  essentially  of  a  disconnect  shunted  by  a  fuse  of  low 
amperage  and  provided  with  a  lock,  so  that  the  disconnect 
cannot  be  opened  unless  the  fuse  is 
in  place.  If  the  disconnect  is  opened 
when  it  is  carrying  current,  the  cur- 
rent is  shunted  through  the  fuse  where 
it  is  interrupted  when  the  fuse  blows 
due  to  the  current  being  above  the 
rated  current  of  the  fuse. 

Mountings. — A  number  of  types  of 
mountings  for  S.  &  C.  fuses  have 
been  developed  by  Schweitzer  & 
Conrad,  Inc.  and  the  Delta-Star 
Electric  Company.  Various  types 
are  furnished  for  both  indoor  and 
outdoor  service,  including  many 
combinations  for  installing  the  fuses 
with  choke  coils,  disconnecting 
switches,  etc.  For  outdoor  service, 
the  fuse  is  mounted  on  a  pair  of 
petticoat  insulators  mounted  hori- 
zontally, vertically,  or  at  an  angle  of 
45  degrees.  Similar  outdoor  arrange- 
ments, utilizing  General  Electric  Ex- 
pulsion Fuses  are  shown  in  Fig.  25. 
The  fuse  holder  for  expulsion  type 
fuses  is  made  of  porcelain,  designed  to 
give  high  mechanical  strength.  At 
each  end  are  placed  contact  elements, 
which  engage  the  stationary  contacts 
of  the  mounting.  The  upper  end  is 
closed,  the  lower  end  open. 

The  fuse  wire  is  passed  through  the  holder  and  connected  to  the 
brass  contacts  at  both  ends.  At  the  upper  or  closed  end  of  the 
holder,  the  fuse  cross-section  is  reduced  insuring  that  the  fuse 
melts  at  this  point.  Melting  of  the  fuse  generates  gas,  which 


FIG.  25. — Delta-Star   outdoor 
fuse  arrangement. 


AUTOMATIC  PROTECTION  AND  FUSES  33 

expands  and  explosively  forces  the  arc  downward,  expelling  it 
through  the  lower  or  open  end  of  the  holder,  thus  rupturing  the 
circuit. 

Fused  Breaker. — The  fused  type  circuit  breaker  is  a  modifica- 
tion of  the  carbon  circuit  breaker  that  has  been  used  to  quite  a 
large  extent  in  connection  with  moderate  capacity  high  voltage 
circuits. 

This  circuit  breaker  is  designed  for  potentials  from  6000  to 
60,000  volts.  The  circuit  breaker  consists  of  two  hardwood 
poles,  one  being  longer  than  the  other,  mounted  upon  porcelain 
petticoat  insulators,  to  which  are  secured  the  terminals  for  the 
main  leads  or  wires.  The  wood  poles  are  connected  by  a  hinge, 
so  that  their  extremities  are  in  line  at  the  upper  end.  On  the 
upper  end  of  each  pole  is  mounted  a  copper  sleeve  supporting 
a  round  carbon  contact  block  with  a  hole  through  its  center. 
The  longer  pole  is  provided  with  spring  jaws  or  clips  so  that  it 
may  be  quickly  and  easily  attached  to,  or  detached  from,  the 
terminals  on  the  insulators.  The  short  pole  has  a  flexible  wire 
running  through  its  interior;  this  wire  is  connected  to  the  copper 
sleeve  at  the  upper  end  of  the  short  pole  and  to  the  lower  clip 
terminal  on  the  long  pole.  The  sleeve  at  the  upper  end  of  the 
long  pole  is  connected  to  the  upper  clip  terminal.  These  connec- 
tions make  the  sleeves  at  the  upper  ends  of  the  two  poles  the 
terminals  of  the  apparatus. 

Early  Type. — In  the  earliest  type  of  fused  circuit  breaker  the 
fuse  of  aluminum  wire  was  exposed  in  the  air  and  it  was  neces- 
sary to  allow  ample  space  above  it  for  the  arc  to  rise  and  dissipate 
itself.  For  the  lower  voltages  the  marble  base  was  depended 
on  for  insulation  while  for  the  higher  voltages  the  marble  base 
was  mounted  on  insulators.  These  fused  switches  were  used  in 
considerable  number  in  some  of  the  earlier  Interurban  Railway 
Substations  filling  the  demand  for  a  moderate  priced  high  voltage 
overload  breaker  to  give  automatic  protection  on  the  high  ten- 
sion side  of  the  transformers. 

Latest  Type. — The  latest  modification  of  this  device  as  shown 
in  Fig.  26  has  the  marble  base  replaced  by  petticoat  insulators 
mounted  on  long  pins. 

Construction. — The  fused  type  circuit  breaker  is  lightly,  yet 
strongly  constructed.  The  circuit  breaker  mechanism  consists 
of  a  long  hardwood  pole  on  which  is  mounted  a  movable  arm  con- 
sisting of  a  reinforced  fuse  tube.  At  the  bottom  of  the  fuse  tube 


34          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


FIG.  26. — Fused  circuit  breaker. 


is  a  brass  expulsion  chamber  which  is  connected  to  the  lower  ter- 
minal of  the  breaker  by  a  flexible  copper  shunt.     Attached  to 

the  top  of  the  pole  and 
forming  the  upper  cir- 
cuit-breaker terminal 
there  is  a  brass  bracket, 
with  a  groove  along  its 
top,  which  supports  the 
fuse,  and  a  wing  nut  to 
hold  the  end  of  the  fuse 
when  the  breaker  is 
closed.  The  fuse  passes 
from  the  wing  nut  over 
the  bracket  and  down 
through  the  fuse  tube 
to  the  expulsion  chamber 

where  it  is  attached  to  the  screw-plug  terminal  shown  in  the  end 

of  the  expulsion  chamber. 
S.  &  C.  Breaker.— Still  another 

type    of   high    voltage    breaker 

based  on  the  same  principles  as 

the  S.  &  C.  Fuse  is  made  by 

Schweitzer  &  Conrad,  Inc.  and 

is  shown  in  section  in  Fig.  27. 
Construction. — T  he     s  wi  t  c  h 

consists  essentially  of  a  moving 

contact  mounted  on  the  end  of 

a  spring  actuated  operating  rod, 

and    of    a    stationary    contact 

mounted  in  the  base  of  the  circuit 

breaker,    and  so  arranged  that 

when  the  moving  contact  reaches 

the  closed  position,  the  two  con- 
tacts engage  each  other.     The 

current    is    conveyed     to     the 

moving  contact  through  flexible 

copper  connections  so  that  the 

current  carried   by   the   spring 

is  negligible.     Mounted  on  the 

end   of  the  operating  rod  and    next    to    the    moving    contact 

is  the  liquid  director,  a  funnel-shaped  arrangement  that  forces 


Flexible 

Cable 

FRONT  VIEW  OF 
ilHCUIT  C.REAKER 
IN  CLOSED 
POSITION     Beplaceable 
Contacts 


FlG 


27.  —  S.    &    C.    high    voltage 
breaker. 


AUTOMATIC  PROTECTION  AND  FUSES  35 

a  powerful  stream  of  the  liquid  onto  the  moving  contact  as  it 
recedes  through  the  liquid  when  opening.  Immediately  under 
the  stationary  contact  is  the  excess  pressure  vent  which  opens 
when  the  pressure  in  the  main  tube  becomes  abnormally  high, 
due  to  the  rupturing  of  very  heavy  short  circuits.  This  vent,  as 
well  as  the  two  contacts,  is  very  easily  replaced. 

Latching  Arrangement. — The  operating  rod  which  carries  the 
moving  contact  extends  through  the  top  of  the  circuit  breaker 
and  is  provided  with  a  cross-bar  to  which  the  operating  ropes  or 
other  mechanism  are  attached.  On  top  of  the  switch  is  a  latching 
arrangement  which  holds  the  circuit  breaker  in  the  closed  posi- 
tion. This  latch  is  released  by  a  small  lever  projecting  to  the 
front  which  makes  it  convenient  for  any  method  of  tripping 
that  may  be  chosen. 

Overload  Relay. — Mounted  on  top  of  the  circuit  breaker  is 
the  series  relay  which  provides  the  automatic  overload  feature. 
This  simple  plunger  type  relay  is  calibrated  for  several  values 
above  and  below  the  normal  operating  current  and  will  cause  the 
circuit  breaker  to  open  whenever  the  current  equals  or  exceeds 
the  relay  setting. 

The  liquid  used  in  these  circuit  breakers,  is  a  noninflammable 
liquid  of  a  very  high  dielectric  strength.  It  is  not  only  non- 
inflammable  but  it  is  a  fire  extinguisher,  and  therefore  has  none 
of  the  objectionable  characteristics  of  oil.  It  has  many  of  the 
characteristics  of  Carbon  Tetrachloride,  but  the  boiling  point  is 
very  much  higher  than  that  of  Carbon  Tetrachloride.  It  is 
necessary  to  use  this  liquid  having  a  higher  boiling  point  as 
the  circuit  breakers  are  not  hermetically  sealed  because  of  the 
necessity  for  some  clearance  around  the  operating  rod  where  it 
enters  at  the  top. 


CHAPTER  III 
CARBON  BREAKERS 

Historical. — The  previous  chapter  on  automatic  protection 
gave  an  idea  of  the  various  cases  where  it  is  desirable  to  protect 
circuits  by  means  of  fuses  or  circuit  breakers.  Fuses  were  among 
the  earliest  means  provided  for  securing  automatic  protection, 
particularly  in  D.C.  lighting  plants.  When  the  direct-current 
railway  system  was  started  it  was  soon  found  that  with  500  volts 
or  more,  and  the  fairly  large  currents  that  were  to  be  handled, 
that  fuse  protection  was  not  satisfactory  and  automatic  circuit 
breakers  of  different  kinds  were  designed.  The  earliest  circuit 
breakers  were  practically  knife  switches  with  automatic  features, 
but  the  rapid  burning  away  of  the  contacts  necessitated  some 
means  of  reducing  the  vicious  arcs  that  occurred  when  opening 
the  circuit. 

Carbon  Breakers. — One  of  the  earliest  designs  that  has  stood 
the  test  of  time  is  a  circuit  breaker  with  auxiliary  carbon  con- 
tacts. These  auxiliary  contacts  remain  closed  until  the  main 
contacts  open  and  the  carbons  take  the  final  arc.  The  fairly 
high  resistance  of  the  carbon  vapor  in  the  arc  and  the  fact  that 
the  vaporized  carbon  was  completely  burned  up  aided  in  the 
satisfactory  operation  of  this  device. 

The  principal  demand  for  circuit  breakers  is  to  have  them  open 
the  circuit  when  the  current  reaches  a  certain  predetermined 
value,  and  breakers  are  designed  with  this  end  in  view.  They 
are  also  built  for  underload  conditions  to  open  on  minimum  cur- 
rent, for  overvoltage  to  open  when  the  voltage  exceeds  a  certain 
amount,  for  undervoltage  to  open  when  the  voltage  falls  below 
a  certain  minimum  value  and  for  reversal  when  the  current 
flows  through  the  breaker  in  the  opposite  direction  from  that 
which  was  intended.  It  is,  of  course,  possible  to  combine  these 
various  features  of  overload,  underload,  reversal,  etc.,  in  one  and 
the  same  breaker. 

Owing  to  the  impossibility  of  illustrating  all  capacities  and 
types  of  carbon  break  circuit  breakers,  the  general  features  of 

36 


CARBON  BREAKERS  37 

carbon  break  circuit  breakers  are  considered  in  considerable 
detail  and  the  distinctive  features  of  different  makes  are  illus- 
trated by  examples  of  a  few  representative  ones. 

Space  Required. — The  modern  tendency  is  to  economize  in 
space  wherever  possible.  So  much  apparatus  must  be  installed 
in  so  little  space  that  it  is  often  necessary  to  choose  the  smaller 
of  two  similar  pieces  of  apparatus.  A  circuit  breaker  that  gives 
the  required  performance,  and  at  the  same  time  is  small,  often 
means  considerable  saving  in  space. 

Desirable  Features. — It  is  essential  that  there  be  good  contact 
between  the  current-carrying  parts  of  a  breaker  in  order  to 
obtain  the  maximum  current  rating.  Poor  contact  produces 
local  heating.  A  millivolt  drop  as  low  as  possible  is  desirable  in 
a  circuit  breaker.  This  is  best  obtained  by  having  perfect 
contacts  and  current-carrying  parts  of  ample  size. 

The  carrying  capacity  of  a  breaker  depends  on  the  contact 
and  conductivity  losses,  the  degree  of  ventilation,  and  the  allow- 
able temperature  rise.  The  last  point  is  of  special  significance. 
In  comparing  the  capacities  of  different  breakers,  the  allowable 
temperature  rise  must  be  taken  into  account  in  order  to  provide  the 
same  basis  of  rating  for  each  breaker;  otherwise  the  ratings  will 
not  afford  a  true  comparison  of  capacities. 

In  order  that  a  circuit  breaker  may  give  the  best  service  it  must 
be  easy  closing.  To  obtain  good  service  on  the  system,  the 
breaker  must  be  "positive  holding,"  that  is,  when  it  is  closed, 
it  must  stay  closed  until  tripped  by  one  of  its  tripping  devices. 
Vibration  or  stray  fields  should  not  open  it.  When  a  breaker 
opens,  whether  tripped  by  the  operator,  by  overload,  or  by  any 
other  means,  it  is  absolutely  essential  that  its  release  be  positive 
and  quick  so  that  it  breaks  the  circuit  instantly.  It  should 
never  open  sluggishly. 

Dust  and  other  foreign  particles  are  liable  to  lodge  on  the  con- 
tacts of  carbon  circuit  breakers.  Repeated  openings  of  the 
breaker  under  load  will  burn  the  contacts  slightly,  making  them 
rough.  In  order  that  the  dust  may  be  cleaned  off  and  that  the 
slightly  rough  surface  may  be  kept  smooth,  a  breaker  should 
have  a  self-cleaning  action,  that  is,  its  contacts  should  be  so 
arranged  that  there  is  a  slight  wiping  action  between  them 
when  they  are  being  opened  and  closed. 

A  circuit  breaker  should  be  easily  adjusted,  but  when  set,  its 
adjustment  should  be  permanent  until  changed  by  the  operator. 


38          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

A  circuit  breaker  must  be  reliable.  It  should  have  positive 
operation  under  all  conditions.  Better  have  none  on  the  line 
at  all  than  have  one  that  cannot  be  depended  upon. 

Temperature. — The  current-carrying  parts  adjacent  to  the 
contact  surfaces  of  carbon  circuit  breakers  should  carry  their 
full-rated  current  continuously  with  a  maximum  temperature 
rise  of  either  20  degrees  or  30  degrees  Centigrade,  above  the 
temperature  of  the  surrounding  atmosphere. 

The  20-degree  rise  basis  is  recommended  when  the  maximum 
temperature  of  the  air  where  the  breaker  is  located  may  approxi- 
mate 40  degrees  Centigrade  and  the  load  is  practically  continuous 
as  on  generator,  converter,  or  transformer  circuits. 

The  30-degree  rise  basis  is  recommended  where  the  maximum 
temperature  of  the  air  where  the  breaker  is  located  may  approxi- 
mate 30  degrees  Centigrade  or  less,  or  the  load  is  intermittent, 
as  on  feeder  circuits. 

The  insulated  coils  of  most  carbon  circuit  breakers  will  carry 
their  full-rated  current  continuously  with  a  maximum  tempera- 
ture rise. of  50  degrees  Centigrade  above  the  temperature  of  the 
surrounding  atmosphere. 

Current  Ratings. — The  current  ratings  shown  for  all  carbon 
circuit  breakers  listed  in  makers'  catalogues  are  maximum  based 
on  the  allowable  temperature  rise  that  is  reached  after  a  continu- 
ous run  of  approximately  one  hour  or  more  at  the  rated  current. 
Inasmuch  as  a  circuit  breaker  reaches  its  final  temperature 
quickly  with  steady  current  load,  it  is  necessarily  a  maximum 
rated  device.  In  selecting  a  breaker,  it  is,  therefore,  recommended 
that  the  rated  capacity  should  be  at  least  as  great  as  the  maxi- 
mum rated  one-hour  (or  more)  overload  current  of  the  apparatus 
that  the  breaker  will  be  required  to  control.  Owing  to  the 
"skin-effect"  and  eddy-current  heating  in  alternating-current 
conductors,  a  circuit  breaker  with  the  same  rise  in  temperature 
has  a  lower  alternating-current  rating  than  direct-current  rating. 
Also,  on  25-cycle  service  a  circuit  breaker  above  300-ampere 
rating  will  carry  continuously  considerably  more  than  its  60- 
cycle  rating. 

Interrupting  Capacity. — While  the  interrupting  capacities  of 
most  of  the  high-grade  carbon  breakers  meet  the  requirements  of 
the  National  Electrical  Code,  and  in  certain  cases  are  much 
greater,  it  should  be  noted  that  the  smaller  types  of  various 
manufacturers  should  not  be  connected  too  closely  to  apparatus 


CARBON  BREAKERS  39 

or  bus  bars  capable  of  delivering  larger  amounts  of  power  than 
specified  by  the  Code.  The  relatively  small  wires  ordinarily 
used  to  connect  these  lower-capacity  circuit  breakers  with  sources 
of  power  should  be  sufficient  to  introduce  enough  resistance  to 
limit  the  current  that  can  be  drawn  through  the  breaker  under 
short-circuit  conditions  to  the  amount  specified  by  the  Code. 

Intricate  mechanism  in  a  circuit  breaker  means  endless  trouble. 
Simplicity  should  be  looked  for  in  every  part. 

Accidents  that  cannot  be  foreseen  are  always  liable  to  happen, 
and  repairs  must  be  made  sometimes  to  the  best  breaker.  A 
circuit  breaker  should  be  so  designed  as  to  facilitate  repairing, 
and  thus  cause  the  least  possible  delay  in  putting  it  back  in 
service. 

Distinctive  features  of  the  best  types  of  carbon  circuit  breakers 
are:  exceptional  ruggedness  and  neatness  of  appearance;  sim- 
plicity of  construction,  operation,  and  installation;  few  parts, 
all  easily  accessible,  and  those  parts  likely  to  require  replace- 
ment, easily  renewable;  great  compactness,  thus  saving  in 
space;  long  rigid  carbon  arms,  giving  long  break  of  arcing 
members;  current-carrying  parts  of  ample  size  so  that  no  portion 
of  breaker  will  exceed  guaranteed  temperature  rise;  main 
moving  contacts  are  laminated  copper  brushes,  self-wiping  or 
self-cleaning;  auxiliary  contacts  in  addition  to  main  contacts; 
self-aligning,  self-cleaning  carbon  contacts;  contact  pressure 
adjustable;  low  resistance  from  main  contacts  to  carbon-arcing 
contacts;  small  millivolt  contact  drop;  very  simple  toggle 
mechanism;  all  breakers  trip  easily,  quickly  and  positively; 
auxiliary  tripping  and  signalling  attachments  are  easily  applied. 

Construction. — In  high-grade  carbon  circuit  breakers  special 
attention  has  been  given  the  problem  of  keeping  the  size  of 
breakers  down  to  a  minimum  for  the  required  performance. 
The  construction  is  such  that  the  best  possible  ventilation  is 
secured,  the  object  being  to  obtain  the  maximum  radiating  sur- 
face on  all  current-carrying  parts,  and  thus  insure  a  breaker  of 
the  highest  current-carrying  capacity  for  its  size. 

On  the  mechanically  operated  breakers,  the  closing  mechanism 
consists  of  the  operating  handle  and  the  toggle  mechanism  con- 
necting the  handle  lever  and  the  main  contact  arm.  On  the 
electrically  operated  breakers,  the  closing  is  usually  effected  by 
means  of  a  direct-current  solenoid  mounted  below  the  main 
mechanism.  The  solenoid  plunger  is  connected  to  the  closing 


40          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

mechanism  in  such  a  way  that  when  current  flows  through  the 
solenoid  and  the  plunger  is  drawn  into  the  solenoid,  the  main 
contacts  are  closed. 

The  contacts  of  these  breakers  are  held  closed  automatically 
by  a  trigger  or  latch.  The  various  trip  mechanisms  are  con- 
structed to  disengage  this  latch  and  permit  the  breakers  to  open. 

Main  Contacts. — All  current-carrying  contacts  are  made  of 
copper.  The  movable  element  is  a  laminated  brush  composed  of 
several  strips  of  copper  and  makes  an  end-on,  or  butt,  contact 
with  the  fixed  element;  this  gives  a  relatively  large  wiping,  or 
self-cleaning  contact  when  the  breaker  is  closed  and  insures  uni- 
form pressure  over  the  entire  contact  surface.  A  high  contact 
pressure  is  obtained  because  of  the  form  of  mechanism  between 
the  handle  and  contacts.  This  pressure  reduces  the  heating  of 
the  contacts  to  a  minimum  and  secures  a  low  contact-resistance. 
A  means  is  provided  for  adjusting  this  contact  pressure  and  for 
equalizing  the  pressure  on  both  ends  of  the  moving  element. 

The  main  contact  block,  or  fixed  element,  and  the  terminal 
stud  are  of  two  forms:  the  round  threaded  form  and  the  slotted- 
bar  or  laminated  form  for  laminated  connections.  In  the 
smaller  capacities  below  2500  amperes,  direct  current,  they  are 
made  up  of  drawn  round  or  rectangular  copper  bar  stock,  elec- 
trobrazed  to  form  the  terminal  stud  and  contact  blocks.  In  the 
larger  capacities,  higher  than  2000  amperes,  direct  current,  they 
are  "pressure  moulded"  of  extremely  high-conductivity  copper, 
or  made  with  laminated  copper  bars. 

The  slotted-bar  studs  are  arranged  with  slots  to  take  lamina- 
tions running  either  vertically  or  horizontally,  or  with  one  stud 
with  vertical  and  the  other  stud  with  horizontal  slots,  thus 
allowing  the  connections  to  the  bus  bars  to  be  made  in  the  most 
convenient  manner. 

METHODS  OF  OPERATION 

Under  average  conditions,  for  simple  plants  having  not  over 
10,000-ampere  750-volt  units,  carbon  circuit  breakers  can  be 
mounted  directly  on  the  switchboard  panel.  Where  the  require- 
ments exceed  these,  remote-controlled  breakers  mounted  apart 
from  the  panel  and  electrically  controlled  from  the  panel  by  an 
auxiliary  circuit  become  advisable.  For  1500- volt  service  in 
capacities  up  to  2500  amperes  the  single-pole  manually  operated 
remote-control  breakers  are  recommended.  Electrically  oper- 


CARBON  BREAKERS  41 

ated  remote-controlled  breakers  are  also  made  for  lower  capaci- 
ties for  applications  where  for  other  reasons  it  is  preferred  not  to 
mount  the  breaker  directly  on  the  panel. 

Manual  Operation. — Manual  closing  by  a  handle  connected 
directly  to  the  breaker  is  the  ordinary  method  of  closing  carbon 
circuit  breakers.  Pulling  down  on  the  handle  closes  the  breaker. 

Electric  Operation. — In  the  field  of  power  operated  carbon 
circuit  breakers  the  Westinghouse  Electric  &  Manufacturing 
Company  and  the  General  Electric  Company  adopted  as  stand- 
ard the  direct-current  electrical-solenoid  magnet  method  of 
closing.  The  Cutter  Company  use  various  other  methods,  such 
as  motor,  hydraulic  and  pneumatic  closing  in  addition  to  sole- 
noids. 

Solenoid  operated  carbon  circuit  breakers  of  one  design  are 
closed  by  means  of  a  simple  cylindrical  magnet  mounted  below 
the  breaker  mechanism.  The  solenoid  is  equipped  with  a  dash- 
pot  device  that  takes  care  of  the  shock  at  the  end  of  the  closing 
operation,  and  yet  permits  the  breaker  to  close  quickly.  When 
the  closing  switch  is  thrown,  current  flows  through  the  solenoid 
and  the  plunger  is  drawn  down.  This  closes  the  contacts,  which 
are  held  closed  automatically  by  a  latch.  The  solenoid  plunger 
rises  when  the  closing  circuit  is  opened,  so  that  it  will  not  retard 
the  opening  of  the  breaker  when  tripped.  The  breaker  is  opened 
by  the  automatic  overload  trip  or  by  the  shunt-trip  attachment 
mounted  at  the  side  of  the  breaker  mechanism.  The  breakers 
can  be  tripped  manually  by  pushing  up  on  the  operating  handle 
or  back  on  the  insulated  trip  handle  near  the  bottom  of  the 
breaker. 

Standard  closing  coils  are  wound  for  direct  current.  Direct- 
current  mechanisms,  besides  being  simpler  in  construction,  more 
reliable  in  operation,  and  more  easily  kept  in  repair,  are  much 
more  economical  of  space  and  power  than  alternating-current 
mechanisms.  Alternating-current  shunts  and  current  trans- 
former trip  coils  are  available  in  special  cases. 

The  closing  and  tripping  mechanisms  are  operated  by  a  con- 
trol switch  with  or  without  a  control  relay  in  the  operating  cir- 
cuit, and  usually  with  signal  lamps.  The  electric  operating 
mechanism  has  a  small  double-throw  switch  to  operate  the  signal 
lamps  and  to  open  the  shunt-trip  coil  circuit  when  the  circuit 
breaker  has  opened. 


42          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Acceleration. — On  account  of  the  reaction  of  the  laminated 
moving  contact  members,  no  separate  means  of  accelerating  the 
breaker  to  its  open  position  are  necessary.  The  laminated  mem- 
bers, which  act  as  powerful  springs,  the  toggle-lever  springs,  the 
secondary-contact  springs,  and  the  carbon-arm  springs,  all  serve 
to  accelerate  the  opening  of  the  breaker. 

In  general,  carbon  circuit  breakers  are  made  for  either  panel  or 
separate  mounting.  For  separate  mounting  they  are  usually 
furnished  mounted  on  a  slate  base  with  black  marine  finish. 

Non-automatic  breakers  are  simply  switches  capable  of  opening 
overloads,  but  opened  and  closed  only  at  the  desire  of  the  opera- 
tor. They  can  be  made  automatic  through  relays  operating  on 
a  shunt-trip  coil. 

Tripping  Methods. — All  standard  overload-trip  carbon  circuit 
breakers  are  plain-automatic,  that  is,  when  closed  with  an  over- 
load on  the  line,  they  will  remain  closed  as  long  as  the  closing 
handle  is  held  down  or  the  closing  coil  is  energized,  but  will  not 
remain  closed  when  the  handle  is  released  or  the  closing  cir- 
cuit is  opened. 

Full-automatic  overload-trip  breakers  trip  free  of  the  handle 
so  that  they  cannot  be  held  closed  on  a  short  circuit  or  overload. 

All  standard  overload-trip  carbon  breakers  are  arranged  for 
direct  acting  (series)  tripping  without  relays.  In  some  cases 
breakers  used  on  alternating-current  circuits  are  supplied  for 
transformer  tripping.  Breakers  used  on  alternating-current 
circuits  and  equipped  with  shunt-trip  coils  can  be  made 
transformer-trip  through  relays  acting  on  the  shunt-trip  coils. 

Calibration. — The  standard  range  of  calibration  for  automatic 
overload-trip  varies  with  different  makes.  A  typical  range  is  from 
80  to  160  per  cent,  of  the  30-degree  rise  ampere  rating.  Breakers 
can  readily  be  set  to  trip  at  any  point  within  their  range.  Cali- 
bration higher  than  standard  can  be  furnished  in  most  cases. 

SPECIAL  ATTACHMENTS 

Shunt-trip  Attachment. — The  shunt-trip  attachment  enables 
the  breaker  to  be  tripped  electrically  from  some  distant  point. 
A  direct-current  shunt-trip  mechanism  is  included  as  standard 
with  each  electrically  operated  breaker  and  can  be  supplied  as  an 
accessory  on  almost  all  manually  operated  breakers.  If  the  cir- 
cuit breaker  is  not  arranged  to  cut  out  the  shunt-trip  circuit, 
signal  contacts  should  be  provided  to  do  this  when  the  circuit 


CARBON  BREAKERS  43 

breaker  trips,  as  the  tripping  coils  are  designed  for  intermittent 
service  only.  The  automatic  undervoltage-trip  attachment 
when  supplied  with  a  suitable  resistor,  can  be  used  as  a  shunt- 
trip  mechanism  by  momentarily  short-circuiting  the  coil. 

Inverse  Time  Limit  Attachment. — An  inverse  time  limit  dash- 
pot  with  an  adjustable  time  feature  can  be  used  with  some 
breakers.  This  attachment  will  cause  the  breaker  to  trip  al- 
most instantly  on  heavy  overload  and  much  more  slowly  on 
light  overloads,  giving  the  circuit  on  light  overload  the  chance  to 
clear  the  trouble  before  the  breaker  trips. 

Automatic  Undervoltage-trip  Attachment. — The  undervoltage- 
trip  attachment  is  used  to  trip  the  breaker  when  the  line  voltage 
fails  or  falls  approximately  50  per  cent,  or  more  under  the  rated 
normal  voltage.  It  is  of  particular  advantage  in  automatically 
disconnecting  a  motor  from  the  circuit  at  the  time  of  temporary 
interruption  of  the  supply  circuit,  for  should  the  motor  come  to 
rest  and  still  be  connected  to  the  line  it  would  be  subjected  to  full 
voltage  upon  the  power  being  restored.  The  automatic  under- 
voltage-trip attachments  for  carbon  circuit  breakers  are  reset  by 
hand  or  automatically  on  the  opening  of  the  breakers  according 
to  requirements. 

Only  one  undervoltage  attachment  is  necessary  with  multipole 
breakers.  No  additional  protection  is  afforded  by  the  use  of  a 
coil  across  each  phase  of  a  2-phase  or  3-phase  circuit  for 
the  reason  that  the  motors,  when  the  voltage  of  one  phase  fails, 
will  run  single  phase  and  feed  back  into  the  idle  phase,  thus 
preventing  the  undervoltage  device  from  acting;  but  the  resulting 
overload  on  the  working  phase,  due  to  the  entire  load  being  on 
that  phase,  will  trip  a  properly  set  breaker. 

The  undervoltage-trip  attachment,  if  supplied  with  suitable 
resistor,  can  be  used  also  as  a  shunt-trip  attachment  by  momen- 
tarily short-circuiting  the  coil. 

Automatic  Re  verse -current  Trip  Attachment. — This  attach- 
ment is  particularly  applicable  to  storage-battery  charging,  or  the 
operation  of  direct-current  generators  or  synchronous  converters 
in  parallel,  its  function  being  to  disconnect  the  generator  from  the 
bus  whenever  the  current  reverses  due  to  any  cause,  as  for  ex- 
ample, rise  in  battery  voltage,  drop  in  generator  voltage,  or 
stopping  of  the  prime  mover.  It  is  not  affected  by  an  overload 
in  the  normal  direction,  and  can  be  applied  to  non-automatic 
breakers  where  the  reverse-current  protection  only  is  desired. 


44          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

The  automatic  reverse-current  trip  attachment  automatically 
resets  itself  after  the  tripping  operation  and  is  prompt  and 
reliable  in  its  action.  Two  windings  are  provided,  one  shunt  and 
the  other  series,  the  former  having  a  shunt  cut-out  which  auto- 
matically opens  the  circuit  when  the  breaker  trips.  If  desired, 
the  tripping  current  may  be  obtained  from  a  circuit  other  than 
that  in  which  the  circuit  breaker  is  connected. 

The  tripping  range  can  be  easily  adjusted.  If  the  shunt 
coil  is  supplied  with  normal  voltage,  the  Westinghouse  attach- 
ment can  be  set  to  trip  the  breaker  at  any  current  value  from  about 
5  per  cent,  of  normal  rating  in  the  positive  direction  to  25  per 
cent,  of  normal  rating  in  the  negative  or  reverse  direction.  The 
amperes  required  to  trip  the  breaker  will  be  affected  only  slightly 
by  small  changes  in  voltage. 

Automatic  Overvoltage-trip  Attachment. — The  automatic  over- 
voltage-trip  attachment  is  used  principally  in  connection  with 
storage-battery  charging,  where  it  is  desired  to  cut  off  the  current 
supply  when  the  battery  becomes  fully  charged.  It  may,  how- 
ever, be  used  in  any  alternating-current  or  direct-current  circuit 
which  it  is  desired  to  open  automatically  in  case  of  either  mod- 
erate or  abnormal  rise  in  voltage. 

Automatic  Underload-trip  Attachment. — The  automatic  un- 
derload-trip  attachment  is  principally  used  on  storage-battery 
charging  circuits.  When  the  charging  current  decreases  to  a 
certain  predetermined  value,  the  breaker  is  tripped;  the  circuit 
is  thus  opened  and  the  chance  of  current  flowing  back  from  the 
battery  to  the  generator  and  causing  trouble  is  thus  avoided. 
For  this  application  the  attachment  is  generally  set  to  trip  at 
10  per  cent,  of  normal  load,  but  the  standard  attachments  can  be 
set  to  trip  at  any  point  from  10  to  25  per  cent.  The  automatic 
underload-trip  attachments  are  reset  by  hand  or  automatically 
by  the  opening  of  the  breaker,  according  to  service  desired. 

Signal  Contacts. — For  use  as  shunt-trip  cut-outs  and  in 
operating  signal  lamps,  a  single-pole  double-throw  plunger 
switch  that  automatically  closes  one  signal  circuit  when  the 
breaker  is  closed  and  another  when  it  is  open  is  supplied.  This 
attachment  is  fastened  to  the  panel  and  is  operated  by  an  in- 
sulated rod  actuated  from  the  moving  main-contact  brush  of 
the  breaker.  It  has  a  switching  capacity  carrying  from  10 
amperes  at  125  volts  to  1  ampere  at  750  volts. 


CARBON  BREAKERS  45 

Bell  Alarm  Contacts. — For  this  service  any  small  double- 
throw  single-pole  switch  can  be  used  in  conjunction  with  the 
signal  switch  above  referred  to,  for  indicating  by  lamps,  bells, 
or  other  signal,  the  operation  of  the  breaker.  The  signal  contact 
switch  is  connected  as  a  single-pole,  double-throw  switch  and, 
in  conjunction  with  the  single-pole,  double-throw,  bell  alarm 
cut-out  switch,  makes  the  necessary  connections  to  ring  a  bell  or 
operate  a  signal  when  the  breaker  is  in  the  position  opposite  that 
desired  by  the  operator. 

Relays. — Where  a  more  reliable  time  limit  is  required  for 
selective  operation  of  circuit  breakers  than  can  be  provided  by  the 
type  of  dashpot  described  above,  protective  relays  should  be  used 
in  connection  with  the  circuit-breaker  shunt-trip  coils.  The  use 
of  relays  in  connection  with  an  auxiliary  source  of  direct-current 
power  for  tripping  obviates  the  use  of  overload  coils  and  time 
limit  features  on  the  circuit  breaker. 

Field-Discharge  Contact. — A  combined  shunt-trip  and  field- 
discharge  contact  is  usually  supplied  with  the  2-pole  form 
of  breaker  for  use  in  connection  with  exciter  generators  or 
as  main  field  switches  to  large  alternating-current  generators. 
In  this  service  the  breaker  is  usually  made  non-automatic  as 
the  excitation  should  only  be  interrupted  at  the  will  of  the 
operator.  Reverse-current  trip  is  sometimes  applied  to  this 
field-discharge  form  of  breaker  when  it  is  used  as  the  exciter- 
generator  main  switch  or  breaker. 

Double-arm  Attachment. — The  double-arm  attachment  elimi- 
nates the  necessity  for  switches  in  series  with  a  2-pole  single- 
handle  breaker  in  low  capacity  and  low  voltage  service  and  at  the 
same  time  affords  automatic  protection  to  the  circuit  throughout 
the  closing  period.  With  this  arrangement,  each  pole  of  the 
breaker  is  closed  independently  and  in  succession,  so  that  the 
pole  first  closed  is  left  free  to  open  while  the  second  or  final  pole 
is  being  thrown  in.  The  breaker  being  closed,  an  overload  in 
either  positive  or  negative  line,  or  both,  will  trip  both  poles  simul- 
taneously. 

Trip-free-on-overload  Attachment. — The  trip-free-on-over- 
load  attachment  (also  known  as  "full-automatic-overload  trip") 
on  a  breaker  makes  it  impossible  to  hold  the  breaker  in  a  closed 
position  while  a  continued  overload  condition  or  short  circuit 
exists  on  the  line. 


46          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Full-automatic  or  "trip-free"  operation,  particularly  on  direct 
hand  controlled  carbon  breakers,  is  not  recommended  for  high- 
capacity  circuits  or  for  service  of  over  250  volts  D.C.,  or  440 
volts  A.C.  Carbon  breakers  should  not  be  closed  on  a  circuit 
under  heavy  load.  Another  switch  should  be  used  to  close  the 
circuit,  especially  under  overload;  otherwise  damage  to  the 
secondary  and  carbon  contacts,  or  injury  to  the  operator,  may 
result. 

In  order  to  cover  the  field  of  carbon  breakers  in  as  complete 
a  manner  as  the  space  requirements  will  permit,  typical  breakers 
of  most  of  the  important  American  builders  are  illustrated  and 
described  without  attempting  to  go  much  into  detail  regarding 
any  one  breaker.  A  few  diagrams  are  included  of  special  cir- 
cuit breaker  features  such  as  the  connections  of  the  "Auto 
Reclosing  Breaker,"  and  the  internal  connections  of  a  motor 
operated  breaker  of  the  Cutter  Company. 

List  of  Makers. — Carbon  break  circuit  breakers  have  been 
made  by  a  great  number  of  different  manufacturers,  but  the  best 
known  ones  are  those  that  have  been  made  by  the  following 
American  Works: 

Automatic  Reclosing  Circuit  Breaker  Company,  Columbus,  O. 

Condit  Electrical  Manufacturing  Company,  Boston,  Mass. 

Cutter  Company,  Philadelphia,  Pa. 

General  Electric  Company,  Schenectady,  N.  Y. 

Roller  Smith  Company,  Bethlehem,  Pa. 

Westinghouse  Electric  &  Manufacturing  Company,  Pitts- 
burgh, Pa. 

AUTO  RECLOSING  CIRCUIT  BREAKER 

Operation. — The  Automatic  Reclosing  Circuit  Breaker  is  a 
magnetically  operated  breaker.  There  are  three  coils  which 
govern  its  action. 

First. — The  operating  coil  O,  which  closes  the  main  contact 
and  holds  the  breaker  closed. 

Second. — The  series,  or  overload  coil,  which  causes  breaker  to 
open  in  case  of  overload. 

Third. — The  trip  coil  T,  which  releases  the  lockout  and  per- 
mits the  breaker  to  reclose. 

The  accompanying  cut,  Fig.  28,  shows  the  theoretical  arrange- 
ment of  circuits  with  the  breaker  in  the  closed  position.  The 
operating  coil  O  is  energized  as  follows:  At  point  A  the  series 


CARBON  BREAKERS 


47 


coil  is  electrically  attached  to  the  main  frame,  and  a  circuit  to 
operating  coil  is  made  through  cut-out  contact  C,  to  pin  B,  to 
resistance  R  —  1,  to  operating  coil  O,  to  fuse  L,  and  to  opposite 
side  of  line  at  M. 

A  high  resistance  R— 1  limits  the  current  to  the  operating 
coil  to  an  amount  just  sufficient  to  hold  the  breaker  in  the  closed 
position  but  not  enough  to  start  it  to  close.  An  arm  G  is  pro- 
vided for  the  purpose  of  shunting  R— 1  out  of  circuit  while  the 
breaker  is  in  the  act  of  closing,  so  that  full  potential  will  be  applied 
to  close  the  breaker.  At  the  instant  breaker  closes,  G  is  opened 
by  the  main  contact  brush  and  held  open  by  latch  H. 


Main  Brush  Contact 


-*-To  Generator 


FIG.  28. — Auto-reclosing  breaker 
— closed  position — diagram  of  con- 
nections. 


FIG.  29. — Auto-reclosing  breaker 
— open  position — diagram  of  con- 
nections. 


Opening. — The  breaker,  being  held  closed  magnetically,  will 
open  either  in  the  event  of  voltage  failure  or  by  the  momen- 
tary opening  of  the  operating  coil  circuit. 

Overload. — When  an  overload  occurs  the  plunger  of  over- 
load coils  is  raised  so  as  to  engage  cut-out  contact  arm  C  and 
cause  it  to  rotate  out  of  contact  with  pin  B.  This  results  in  the 
de-energization  of  coil  O  and  the  breaker  opens. 

Voltage  Failure. — In  case  the  voltage  drops  below  that  neces- 
sary to  maintain  the  magnetic  seal  of  the  operating  plunger,  the 
breaker  drops  open. 

Reclosing. — Fig.  29  shows  the  theoretical  arrangement  of 
circuits  with  the  breaker  in  the  open  position.  After  the  breaker 
has  been  opened  due  to  any  cause,  it  is  necessary  for  trip  coil  T 
to  operate,  and  unlatch  H  so  that  arm  G  will  cut  out  R-l. 
This  allows  full  potential  to  be  applied  to  operating  coil  and  closes 
the  breaker. 

Before  the  trip  coil  can  possibly  act  it  is  necessary  that  the 
dashpot  contact  arm  descend  and  close  the  circuit  at  K.  This 


48          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

provides  a  definite  time  interval  during  which  the  breaker  must 
remain  open  regardless  of  the  cause  of  opening.  While  the  main 
contact  brush  is  open  a  shunt  path  is  formed  from  the  positive 
side  of  the  generator  around  the  main  contacts  through  a  high 
resistance  R-2  and  a  low  resistance  R-3. 

Assuming  a  short  circuit  remains  on  the  line  and  the  dashpot 
has  settled  down  so  as  to  complete  the  circuit  for  the  trip  coil,  a 
current  I  will  flow  through  R-2.  The  value  of  the  Resistance  R-2 
is  relatively  high  in  comparison  with  that  of  the  trip  coil  and  the 
load  or  short  circuit  and  R-3  which  is  in  parallel  with  the  trip 
coil.  For  this  reason  a  practically  definite  amount  of  current 
will  flow  through  R-2  regardless  of  the  load  resistance.  But  the 
division  of  this  current  between  the  trip  coil  and  load  circuit  will 
depend  upon  the  load  or  short-circuit  resistance. 

It  will  be  observed  that  there  are  two  paths  whereby  current 
may  flow  from  point  D  to  point  M.  One  of  the  paths  being 
through  a  low  resistance  R-3  to  load  through  short  circuit,  and 
back  to  M.  The  other  path  is  through  the  trip  coil  and  dash- 
pot  contact  arm  to  point  M.  The  trip  coil  is  wound  with  a  low 
resistance  so  that  a  slight  variation  in  the  short-circuit  resistance 
will  also  cause  a  corresponding  change  of  current  through  the 
trip  coil.  So  long  as  a  short  circuit  of  low  resistance  remains  on 
the  load  circuit  the  greater  part  of  current  I  will  be  shunted 
around  the  trip  coil  through  the  short  circuit,  as  indicated  by 
I".  However,  as  soon  as  the  short  circuit  is  removed  or  the 
resistance  of  the  short  circuit  increased  to  a  value  which  would 
not  permit  an  excessive  current  to  flow  were  the  breaker  to 
reclose,  enough  current  I  will  be  forced  through  the  trip  coil  to 
cause  its  armature  to  rise  and  release  latch  which  results  in  the 
closing  of  breaker,  after  which  the  parts  assume  the  position 
shown  in  Fig.  28.  The  breaker  does  not  close  or  attempt  to  close 
while  a  short  circuit  or  overload  of  low  resistance  exists,  but  does 
close  instantly  and  automatically  upon  the  removal  of  short 
circuit  or  overload. 

Types. — These  breakers  are  made  in  three  different  types, 
depending  on  the  current  ratings.  The  smallest  ones  made 
in  capacities  of  25  to  400  amperes  are  intended  for  the  protection 
of  branch  circuits  and  have  contacts  of  solid  copper  with  graphal- 
loy  arcing  tips  to  take  the  final  break.  The  medium  size  for 
ratings  from  300  to  800  amperes  have  laminated  copper  brush 
main  contacts,  with  secondary  contacts  of  copper  and  graphalloy 


CARBON  BREAKERS 


49 


contacts  to  take  the  final  break.     The  largest  size,  shown  in  Fig. 

30,  has  contacts  similar  to  the  medium  sized  one.     The  operating 
coil  and  trip  coil  are  completely  housed 

and  protected  in  a  cast-iron  frame  which 
carries  the  operating  mechanism.  These 
breakers  are  built  in  capacities  from 
1200  to  2000  and  modifications  of  this 
type  are  built  for  3000  and  4000  amperes. 
These  breakers  are  used  for  the  pro- 
tection of  independent  feeder  circuits, 
generator  circuits,  feeders  in  a  network, 
or  for  sectionalizing  circuits  and  can  be 
arranged  to  take  care  of  the  many  con- 
tingencies in  an  automatic  substation  or 
a  plant  where  the  class  of  attendance  is 
poor. 

CONDIT  CIRCUIT  BREAKERS 

Type  K-2  breakers  illustrated  in  Fig. 

31,  are  made  both  front  and  rear  con- 
nected in  capacities  up  to  300  amperes 
at  600  volts  B.C.  or  750  volts  A.C.  with 
underload    trip,   overload    trip,  under- 
voltage  trip,  shunt  trip,  reverse  power    Large  size. 


FIG.  31. — Condit  Electric  Mfg.  Co.  circuit  breaker  type  K-2. 

and  time  limit.     Various  combinations  of  these  different  methods 
of  tripping  may  be  applied  to  the  same  breaker.     These  breakers 


50          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

are  usually  made  hand  operated  but  can  be  made  electrically 
operated. 

Construction. — While  the  K-2  air  circuit  breaker  has  been 
primarily  designed  for  industrial  application,  its  finish  and  general 
appearance  are  such  that  it  harmonizes  well  with  instruments 
and  devices  usually  associated  with  switchboards. 

It  consists  essentially  of  three  distinct  standard  units:  (1) 
the  upper  contact  member  with  its  auxiliary  metal  and  carbon 
contacts,  stud  and  nuts;  (2)  the  movable  contact  members, 
comprising  the  brush  with  its  metal  and  carbon  auxiliary  contacts 
and  the  operating  mechanism,  supported  by  the  housing;  (3) 
the  tripping  coil  with  its  stud,  magnetic  circuit  and  calibration 
plate. 

The  conducting  parts  are  liberally  designed,  and  the  laminated 
brush  is  fully  protected  by  relatively  massive  carbon  auxiliaries 
on  which  the  arc  is  finally  broken.  Interposed  between  the 
laminated  brush  and  the  carbon  contacts  is  a  metal  auxiliary 
contact  so  related  to  the  main  brush  that  proper  protection  to 
the  current-carrying  members  is  assured.  The  carbon  and  metal 
auxiliary  contacts  are  easily  renewable  and  reversible. 

A  vibration  proof  latch  holds  the  breaker  normally  in  the  closed 
position  and  when  released  by  the  tripping  coil  the  moving  con- 
tact member  opens  positively  and  quickly.  The  magnetic  cir- 
cuit of  the  trip  coils  is  laminated.  This  feature  is  of  importance, 
as  it  renders  overload  breakers  interchangeable  for  use  on  either 
direct  or  alternating-current  circuits.  The  breaker  is  easily 
closed  by  a  downward  movement  of  the  handle,  and  the  mechan- 
ism is  so  arranged  that  the  brush  pressure  is  properly  distributed. 

Double-pole  breakers  are  arranged  for  independent  closing, 
but  both  poles  trip  simultaneously  on  overload.  Three-pole 
breakers  are  arranged  with  a  common  handle,  causing  all  poles 
to  be  closed  and  opened  simultaneously.  Four-pole  breakers  are 
not  arranged  so  that  all  poles  are  closed  simultaneously — two  2- 
pole  breakers  are  furnished,  each  having  a  common  handle  which 
causes  the  two  poles  to  be  closed  and  opened  simultaneously. 

Barriers  are  furnished  on  all  multipole  breakers  above  250 
volts  D.C.  or  440  volts  A.C.  - 

Trip  Range. — Standard  overload  breakers,  for  use  on  both  di- 
rect and  alternating-current  circuits,  are  calibrated  from  80  to 
160  per  cent,  of  full-load  current. 

Air  circuit  breakers  which  are  seldom  opened  in  the  course  of 


CARBON  BREAKERS 


51 


regular  operation  should  be  periodically  opened  and  thoroughly 
cleaned. 

Type  K-l  breakers  shown  in  Fig.  32  are  made  in  capacities 
from  100  amperes  to  5000  B.C.,  4400,  25  cycle,  3300,  60  cycle, 
in  1,  2  or  3  poles  and  as  6000  and  8000  ampere  D.C.  single 
pole  for  plain  overload,  plain  shunt  trip  or  undervoltage  with 


FIG.  32. — Condit  type  K-l  carbon  breaker. 

various  attachments  to  secure  time  limit,  reverse  power  or 
other  features.  These  breakers  are  made  with  round  studs  up  to 
the  2000-ampere  D.C.  size  and  with  laminated  studs  for  the  larger 


CUTTER— I.T.E.  CIRCUIT  BREAKERS 

The  Cutter  Company  make  their  "I.T.E."  breakers. in  various 
forms  and  capacities  for  hand  operation  or  electric  control  de- 
pending on  the  class  of  service  for  which  they  are  intended. 
They  adopted  the  "I.T.E"  designation  as  their  earliest  breakers 
were  designed  to  have  an  "Inverse  Time  Element"  as  one  of 
their  principal  features,  the  time  of  tripping  being  in  an  inverse 
ratio  to  the  severity  of  the  short  circuit. 

Types. — For  250-volt  service  in  capacities  from  5  to  300  am- 
peres the  E-l  type  of  breaker  is  furnished  where  compactness 


52          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


FIG.  33. — Cutter  type  LL  carbon  breaker. 


FIG.  34. — Cutter  type  LG  carbon  breaker. 


CARBON  BREAKERS 


53 


is  an  important  feature,  this  breaker  being  on  a  base  only  5% 
inches  wide  and  7  inches  long. 

For  capacities  from  80  to  1250  amperes  at  250  volts  or  less,  the 
type  N-X  is  used.  To  secure  uniformity  of  appearance  on  a 
switchboard  all  of  the  breakers  are  built  on  the  same  frame.  If 
desired  these  breakers  can  be  provided  with  no-voltage  feature, 
shunt-trip  feature,  time  limit  and  bell  ringing  attachments. 
The  breakers  can  be  made  multipole  with  independent  closing 
arms  so  that  they  are  adapted  for  use  on  distributing  circuits 
without  any  switches  in  series  with  them. 

For  use  on  circuits  of  750  volts  or  less  the  L-L  type  is  built  for 
currents  from  200  amperes  up  to  1600  amperes  D.C.  or  1250  am- 
peres A.C.  As  shown  in  Fig.  33  the  brushes  of  laminated  con- 
struction rest  on  the  contact  blocks  at  an  angle,  while  for  the 
larger  L-G  breakers  shown  in  Fig.  34,  made  in  capacities  up  to 
10,000  amperes  D.C.,  the  laminated  brush  is  of  the  end-on  butt  con- 
struction that  is  found  advantageous  in  large  capacity  breakers. 


FIQ.  35. — Cutter  circuit  breaker — sectional  view. 

Operation. — Fig.  35  shows  a  sectional  view  of  a  typical 
"I.T.E."  breaker  and  the  description  of  the  main  parts  of  the 
breaker  and  its  overload  features  may  be  considered  as  that  of 


54          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

a  normal  high-class  American  breaker,  although  those  of  other 
makers  naturally  differ  in  the  details  of  construction. 

The  illustration,  Fig.  35,  shows  the  details  of  one  form  of 
I.T.E.  Circuit  Breaker  Switch  Member.  98  and  50  are  fixed 
terminals  mounted  upon  the  front  of  the  base  or  switchboard. 
The  current  entering  the  instrument  at  50  by  way  of  the  rear  con- 
nection stud  (not  shown),  passes  through  the  overload  coil  50a 
into  the  contact  block  SOB,  thence  it  passes  through  the  lami- 
nated contact  member  or  bridge  16,  into  the  upper  terminal 
and  out  at  the  rear  by  way  of  a  threaded  stud  (not  shown).  A 
by-pass  of  somewhat  higher  electrical  resistance  than  that  of  the 
main  contact  member  is  offered  by  the  flexible  copper  strip  3, 
through  which  the  current  from  the  lower  contact  block  passes 
to  the  spring  plate  30,  thence  to  secondary  metallic  contacts 
69  and  81  and  the  final  or  breaking  contacts  27  and  75,  which 
consist  of  carbon  blocks. 

The  action  in  opening  the  circuit  is  as  follows:  The  laminated 
member  first  moves  out  of  contact  with  the  terminal  98,  co-inci- 
dent with  which  the  current  is  shunted  through  the  secondary 
path  which,  though  of  higher  resistance  than  the  main  contact 
member,  has  sufficient  conductivity  to  prevent  the  formation 
of  any  arc  at  the  main  contacts.  The  circuit  between  the  sec- 
ondary metallic  contacts  69  and  81  is  next  interrupted,  through- 
out which  action  the  carbons  are  maintained  in  full  contact. 
The  circuit  is  finally  broken  by  the  separation  of  the  carbons 
which  are  highly  refractory,  and  upon  which  the  action  of  the 
current  is  not  such  as  to  impair  their  usefulness. 

The  most  widely  used  circuit  breakers  are  those  which  open 
in  the  event  of  overload  or  excessive  current.  The  operation  of 
the  overload  feature  depends  upon  the  volume  of  current  only, 
regardless  of  its  direction  and  is  independent  of  the  voltage  of 
the  circuit. 

Overload  Feature. — One  form  of  I.T.E.  overload  feature  is 
shown.  The  principal  parts  are  an  armature  127  and  magnet 
59  energized  by  a  winding  50a,  carrying  the  main  current  of  the 
circuit  in  which  the  circuit  breaker  is  connected.  The  armature 
is  pivoted  on  pins  128,  and  is  normally  held  by  gravity  out  of 
engagement  with  the  magnet  against  an  adjustable  stop  136, 
and  is  adapted,  when  the  current  exceeds  a  predetermined  value, 
to  be  drawn  forcibly  against  the  magnet,  toward  the  completion 
of  which  movement  it  impinges  upon  the  latch  87,  which  nor- 


CARBON  BREAKERS  55 

mally  holds  the  switch  member  of  the  circuit  breaker  closed 
against  the  action  of  the  opening  springs.  The  normal  or  "at 
rest"  position  of  the  armature  is  subject  to  convenient  adjust- 
ment by  movement  of  the  stop  136,  by  means  of  knob  11,  so  that 
the  distance  between  magnet  and  armature  may  readily  be 
varied,  the  volume  of  current  required  to  move  the  armature  into 
engagement  with  the  latch  being  correspondingly  varied;  the 
closer  the  armature  is  to  the  magnet  the  less  the  current  required 
to  actuate  it  to  trip  the  circuit  breaker.  The  volume  of  current 
which  will  cause  operation  of  the  overload  feature  at  various 
positions  of  the  armature  is  suitably  indicated  along  the  calibra- 
tion scale  13. 

Reversite. — Where  D.C.  generators  operate  in  parallel  or  are 
used  with  a  storage  battery  a  reverse-current  feature  is  usually 
found  advisable  to  cut  off  a  generator  if  the  other  generators  or 
the  battery  tend  to  force  current  into  the  unit.  The  term 
"Reversite"  is  applied  to  these  Cutter  breakers  that  have  this 
reverse-current  feature. 

Remote-control  circuit  breakers  and  switches  have  the  advantage 
that  they  do  not  require  to  be  massed  together  upon  a  single 
switchboard,  but  may  be  located  in  such  a  manner  as  will  afford 
the  most  convenient  and  economical  cable  installation;  for  while 
remote-control  apparatus  may  be  scattered  around  in  various 
parts  of  the  plant  as  conditions  dictate,  the  control  may  readily 
be  brought  to  any  point  determined  upon  as  the  most  convenient 
for  this  purpose.  The  switches  and  indicating  devices  for  con- 
trolling a  large  number  of  circuit  breakers  may  be  placed  upon  a 
bench  board  of  insignificant  dimensions,  so  that  a  large  installa- 
tion may  be  placed,  by  this  means,  virtually  under  the  eye  and 
within  easy  reach  of  a  single  operator. 

Motor  Operated. — The  reliability  of  motor  operated  circuit 
breakers  depends  in  no  small  degree  upon  the  perfection  of 
apparently  minor  details,  and  every  such  feature  is  given  most 
careful  attention. 

The  motor  operated  device  for  closing  a  circuit  breaker  must 
fulfill  two  conditions :  it  must,  regardless  of  voltage  variations  in 
the  control  circuit,  communicate  to  the  circuit  breaker  the  exact 
movement  required  to  latch  it,  and  it  must  instantly  disengage 
from  the  circuit  breaker  when  the  act  of  closing  is  completed. 
As  the  result  of  failure  to  fulfill  either  of  these  conditions  the 
circuit  breaker  would  remain  under  the  restraint  of  the  closing 


56          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

mechanism  and  would  fail  to  respond  properly  to  overload  or 
other  abnormal  condition  which  should  cause  its  opening. 

The  means  employed  to  meet  these  very  exacting  require- 
ments are  indicated  on  Fig.  36,  where  the  essential  working  parts 
of  the  I.T.E.Motor  Operated  Circuit  Breaker  are  diagrammatically 
shown.  The  movement  of  the  motor  in  closing  the  circuit 
breaker  is  communicated  to  a  gear  sector  A  by  means  of  a 
worm  B,  ball  and  socket  jointed  to  an  extension  of  the  arma- 


FIG.  36. — Cutter  circuit  breaker — motor  operated. 

ture  shaft.  The  gear  sector  is  in  turn  connected  by  means  of  a 
link  C  to  the  circuit-breaker  operating  arm.  Except  during 
the  act  of  closing  the  circuit  breaker  electrically,  the  worm  is  held 
out  of  mesh  with  the  gear  sector  by  the  toggle  D,  which  is 
acted  on  by  the  weight  of  the  magnetic  core  M.  This  core  is 
adapted  to  be  lifted  by  the  engaging  coil  E  when  same  is  duly 
energized.  The  circuits  of  both  motor  and  engaging  coil,  which 
is  connected  in  parallel  with  it,  are  under  control  of  the  timing 
switch  F.  The  relations  between  this  switch  and  the  circuit 


CARBON  BREAKERS  57 

breaker  are  such  that  when  the  circuit  breaker  is  open,  the  switch 
is  closed,  and  vice  versa. 

With  the  circuit  breaker  open,  and  the  timing  switch  in  its 
corresponding  closed  position,  the  motor  may  be  brought  into 
operation  from  the  control  station  by  means  of  an  appropriate 
switch  indicated  at  H.  This  starts  the  motor  through  the 
resistance  J,  and  also  energizes  the  engaging  coil,  which, 
through  the  plunger  acting  on  the  toggle  D,  forces  the  worm 
B  into  engagement  with  the  gear  sector  A,  which  in  turn 
communicates  the  movement  of  the  motor  to  the  circuit  breaker 
through  the  link  C.  The  movement  of  the  toggle  D  is  also 
communicated  to  the  localizing  switch  I  which  connects 
the  motor  directly  with  the  control  circuit  and  renders  its  further 
movement  independent  of  the  control  switch.  At  the  comple- 
tion of  the  closing  movement,  the  stop  K  on  the  gear  sector 
comes  into  engagement  with  the  bell-crank  lever  G,  causing 
it  to  open  the  timing  switch,  thus  disconnecting  the  motor  and 
engaging  coil;  the  heavy  core  M  associated  with  the  latter 
is  then  directed  upon  the  toggle  D,  disengaging  the  gears  so 
that  further  movement  of  the  motor  armature  will  not  be  com- 
municated to  the  circuit  breaker.  The  disengagement  of  the 
gears  is  further  insured  irrespective  of  the  action  of  the  timing 
switch  by  the  upper  arm  of  the  bell-crank  lever  being  directed, 
in  its  final  movement,  against  an  extension  N  of  the  toggle, 
forcing  it  into  the  open  position.  Should  the  motor  overtravel 
from  any  cause  whatever,  its  own  excess  movement  thus  serves 
to  disengage  it  from  operative  connection  with  the  circuit 
breaker. 

Should  abnormal  current  condition  exist  upon  closing,  the 
circuit  breaker  is  ready  to  respond  instantly  and  opens  immedi- 
ately without  restraint  or  drag  from  the  operating  mechanism. 
The  final  movement  of  the  circuit  breaker  in  opening  is  com- 
municated through  the  stop  L  to  the  bell-crank  lever,  thus 
closing  the  timing  switch  and  again  placing  the  motor  circuit  in 
condition  to  be  closed  from  the  control  station.  The  position  of 
the  circuit  breaker,  whether  open  or  closed,  is  indicated  by  the 
lamps  associated  with  the  control  switch. 

Solenoid  Operated. — The  magnetically  operated  circuit 
breaker  of  the  overload  type  shown  in  Fig.  37  may  be  closed  on 
normal  load,  but  immediately  releases  if  closed  electrically  on 
overload;  hence,  the  usual  switch  in  series  may  be  omitted,  a 


58 


SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


provision  allowing  the  utmost  simplification  of  switchboard 
construction.  The  cable  installation  in  conjunction  with  direct- 
current  generators  operating  in  parallel  may  often  be  greatly 
simplified  by  using  these  breakers  (made  without  overload 
feature)  as  equalizer  switches.  By  mounting  them  on  pedestals 
alongside  of  the  respective  generators  they  materially  shorten 


FIG.  37. — Cutter  circuit  breaker — solenoid  operated. 

the  equalizer  leads,  rendering  it  unnecessary  to  run  these  cables 
to  the  switchboard.  This  is  of  especial  advantage  where  the 
switchboard  is  located  at  a  considerable  distance  from  the 
generators. 

Among  the  various  mediums  employed  for  the  actuation  of 
mechanical  devices,  none  has  proved  more  reliable  under  a 
wide  variety  of  most  exacting  conditions  than  compressed  air. 
The  air  brake,  the  electro-pneumatic  signal  and  the  pneumatic 
drill  offer  convincing  illustrations  of  this  fact.  Exposed  to 
changing  atmospheric  conditions  and  sometimes  handled  by 
the  roughest  class  of  labor,  they  do  their  work  with  unvarying 
reliability  and  effectiveness. 


CARBON  BREAKERS 


59 


Pneumatically  Operated.— The  I.T.E.  pneumatically  operated 
remote-control  circuit  breaker,  Fig.  38,  embodies  the  simplest 
possible  method  of  controlling  the  circuit  breaker  from  a  dis- 
tance. The  operating  feature  consists  primarily  of  a  double- 
acting  piston  moving  within  a  cylinder,  each  end  of  the  latter 
having  a  valve-controlled  connection  with  the  compressed  air 
supply.  The  circuit  breaker  is  opened  by  a  movement  of  the 
control  valve  in  one  direction  admitting 
air  to  the  upper  end  of  the  cylinder;  the 
closing  of  the  circuit  breaker  is  caused  by 
an  opposite  movement  of  the  control  valve 
admitting  air  to  the  lower  end  of  the 
cylinder. 

The  circuit  breaker  furnished  in  con- 
nection with  the  class  of  control  has  the 
"Autoite"  feature,  allowing  the  switch 
member  to  open  independent  of  the  move- 
ment of  the  closing  arm.  Should  the  at- 
tempt be  made  to  close  the  circuit  breaker 
upon  overload,  it  is  free  to  respond  in- 
stantly and  without  restraint  from  the 
closing  mechanism.  After  it  has  been  so 
opened,  two  movements  of  the  control 
valve  are  necessary  to  close  it;  one  move- 
ment admitting  air  to  the  upper  end  of  the 
cylinder,  forcing  the  handle  lever  into  en- 
gagement with  the  switch  arm;  a  second 
movement  admitting  air  to  the  lower  end 

VT         £ii         i-         ii.         •         -i    cuit  breaker — pneumatic 

of  the  cylinder,  finally  closing  the  circuit  operated, 
breaker.     Where  the  operator  is  sufficiently 
near  the  circuit  breaker  to  have  it  in  view,  the  control  valve 
may  be  operated  by  hand.     Where  the  instrument  is  located 
at  a  considerable  distance  from  the  point  of  operation,  the  valve 
may  be  operated  electrically,  suitable  signals  at  the  point  of 
control  indicating  the  open  and  closed  positions  of  the  circuit 
breaker. 

The  simplicity  and  ruggedness  of  this  type  of  apparatus 
especially  adapts  it  for  use  in  mills  and  foundries;  also  to  in- 
stallations in  which  the  apparatus  is  exposed  to  atmospheric 


FIG.    38. — Cutter  cir- 


60 


SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


Electro-pneumatic. — Fig.  39  shows  a  remote-control  I.T.E. 
circuit  breaker  with  electro-pneumatic  control.  It  is  of  6000- 
amperes  capacity  for  600-volt  service,  and  illustrates  one  of  a 
considerable  number  made  for  a  large  metropolitan  railway  system. 
These  circuit  breakers  are  mounted  in  stations  along  a  portion 
of  the  road  and  form  the  connections  between  successive  sections 
of  the  third  rail.  They  are  used  to  automatically  disconnect 
such  sections  of  the  rail  as  may  be 
grounded  and  to  reconnect  them 
when  normal  conditions-  have  been 
re-established. 

The  system  in  which  these  circuit 
breakers  are  installed  was  already 
supplied  with  compressed  air  equip- 
ment used  for  operating  signals  and 
there  were  also  a  number  of  tele- 
phone cables  available  for  use  as 
control  circuit  wires.  These  condi- 
tions made  the  installation  of  com- 
pressed air  operated  apparatus 
especially  economical  and  had  con- 
siderable weight  in  determining  the 
selection  of  this  type. 

GENERAL  ELECTRIC  CIRCUIT 
BREAKERS 

The  General  Electric  Company 
have  a  very  complete  series  of  carbon 
circuit  breakers  for  various  kinds  of 
service.  For  light  duty  in  isolated 

plants,  the  type  CG  is  furnished  for  A.C.  or  D.C.  service  in 
capacities  from  3-300  amperes  for  voltages  below  550  D.C.  or 
600  A.C.  and  these  can  be  furnished  for  overload,  underload, 
shunt  trip,  reverse  current,  undervoltage  and  combination  of  these. 
Type  CP.— The  CP  breaker  shown  in  Fig.  40  is  a  high-grade 
switchboard  breaker,  made  in  capacities  from  15-1200  amperes 
for  A.C.  or  D.C  service  in  voltages  up  to  650,  with  the  various 
methods  of  tripping  and  the  usual  attachments. 

The  force  applied  to  the  handle  closes  the  breaker  through  a 
simple  strong  toggle  mechanism  which  acts  directly  on  the  brush. 
The  toggle  joint  gives  a  very  heavy  pressure  at  the  brush  with 


FIG.    39. — Cutter    circuit 
breaker —  electro-pneumatic. 


CARBON  BREAKERS 


61 


minimum  pressure  on  the  handle,  making  the  breaker  very  easy 
to  close.  The  heavy  brush  pressure  insures  good  contact  and 
also  assists  in  rapid  opening  when  the  breaker  is  tripped. 


FIG.  40. — General  Electric  Co.  circuit  breaker  type  "CP." 

Contacts. — The  main  brush  is  of  special  form.  Laminations 
make  "end-on"  contact  with  heavy  and  uniform  pressure  over 
entire  contact  surface  without  tendency  to  force  any  part  of 
brush  out  of  contact.  The  cross-sectional  area  of  the  brush 
is  ample  for  the  amount  of  current  it  is  designed  to  carry,  and 
the  form  of  the  brush  permits  the  maximum  pressure  between  the 
laminations  and  the  contact  block. 

A  burning  tip  is  provided  for  each  pole  so  that  burning  of  the 
main  brush  is  prevented.  Burning  tips  close  with  wiping  action. 
They  are  easily  replaced  at  small  expense. 

Secondary  contacts  are  solid  blocks  of  selected  carbon,  shaped 
to  fit  accurately  in  the  holders  to  which,  after  being  copper  plated 


62          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


FIG.  41. — General  Electric  Co.  circuit  breaker  type  CK. 


FIG.  42. — General  Electric  Co.  circuit  breaker  type  "CP3." 


CARBON  BREAKERS 


63 


and  tinned,  the  carbon  contacts  are  securely  sweated.  No  screw 
holes  or  grooves  are  used  in  the  carbons.  The  carbon  contacts 
are  closed  under  pressure  with  a  wiping  motion  which  insures 
good  contact. 


FIG.  43. — 12,000-amp.  G.  E.  carbon-break  circuit  breaker. 

When  the  breaker  opens,  the  brush  first  breaks  contact;  next 
the  burning  tip  and  finally  the  secondary  carbon  contact.  This 
sequence  of  operation  prevents  all  burning  of  main  brush  contacts. 

Type  CK. — The  type  CK  is  a  high-grade  switchboard  breaker 
for  250  volts  D.C.,  1500-6000  amperes  and  for  A.C.  480  volts, 
1500-3500  amperes.  The  CK-2  is  intended  for  650-volt  service 
and  is  built  in  sizes  1500-10,000  amperes  D.C.  and  1500-3500 


64          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


A.C.  These  breakers  are  shown  in  Fig.  41,  the  main  difference 
in  the  two  types  being  in  the  length  of  the  carbon  arms.  Their 
general  features  are  like  the  C.P. 

On  the  CK-2  breaker,  the  arm  carrying  the  carbon  secondary  is 
locked  in  position  under  full  pressure  until  the  main  brush  has 
opened  a  certain  distance,  after  which  the  secondary  contact 
arm  rapidly  swings  forward  and  widely  separates  the  secondary 
contacts.  Current  passing  through  the  breaker  energizes  the 
magnetic  circuit  around  the  lower  stud  and  attracts  the  armature, 
which  strikes  the  latch  a  hammer  blow 
and  trips  the  breaker. 

A  positive  locking  latch  holds  the 
breaker  closed.  Latch  is  so  con- 
structed that  breaker  will  not  jar 
open,  but  will  trip  easily  without  aid 
of  accelerating  devices. 

Solenoid  Operated. — For  solenoid 
operation  the  breakers  are  designated 
as  CP-2  and  CP-3  and  these  contain 
the  same  features  as  the  corresponding 
hand  operated  types.  The  arrange- 
ment of  the  solenoid  mechanism  is 
shown  in  Fig.  42.  The  plunger  of  the 
closing  coil  acts  directly  on  a  simple 
toggle  to  close  the  breaker  and  the 
construction  is  such  as  to  give  a  very 
heavy  pressure  on  the  brush  contacts. 
A  removable  handle  is  conveniently 
located  and  insulated  from  the  live 
parts  of  the  breaker.  A  removable 
handle  is  provided  for  inserting  in  a 
socket  of  the  mechanism  for  hand  closing. 

Heavy  Breakers. — Special  breakers  for  very  heavy  A.C.  cur- 
rents are  usually  made  with  the  solenoids  mounted  separately 
from  the  breaker,  as  shown  in  Fig.  43,  this  being  a  breaker  fur- 
nished to  the  American  Woolen  Company,  at  Lawrence,  Mass., 
to  carry  12,000  amperes  continuously  at  40  cycles,  600  volts. 

Motor  Operated. — An  interesting  combination  of  motor  oper- 
ated carbon  breakers  and  brush  type  of  switch  is  shown  in  Fig.  44, 
of  which  there  were  190  switches  furnished  on  the  original  con- 
tract for  the  substations  of  the  New  York  Central  Railway. 


FIG.  44. — General  Electric 
Co.  circuit  breaker  motor 
operated  with  switch. 


CARBON  BREAKERS 


65 


When  the  control  switch  is  manipulated  on  the  switchboard  the 
motor  is  started  and  the  carbon  break  circuit  breaker  is  closed. 
Further  rotation  of  the  motor  disconnects  it  from  the  breaker 
mechanism  and  connects  it  to  the  switch  mechanism  which  it 
closes  in  turn.  If  there  is  a  short  on  the  circuit  the  breaker  is 
free  to  trip  out  and  open  the  circuit. 

ROLLER-SMITH  CIRCUIT  BREAKER 

The  Roller-Smith  breaker  is  made  in  capacities  of  5  amperes 
to  6000  amperes  for  250  volts  and  600  volts,  multipole  breakers 
being  built  up  to  1000  amperes  and  the  large  ones  being  made 
single  pole  only.  The  breakers  can  be  supplied  for  overload  or 
underload  or  both  and  reverse  current  and  other  features  can  be 
secured  through  relays. 


CROSS-SECTIONAL  VIEW 
FIG.  45. — Roller-Smith  carbon-break  circuit  breaker. 

The  R-S  breaker  shown  in  Fig.  45  is  closed  by  pulling  down  the 
handle  to  the  position  shown  in  cut.  The  arm  is  under  compres- 
sion against  the  brush  and  tends  to  open  on  account  of  the  spring 
of  its  coil,  but  it  is  held  closed  by  the  roller  on  the  handle  (which 
is  slightly  over  the  center  line  between  handle  bearing  and  roller 
on  arm).  A  slight  kick  from  the  armature  knocks  it  back  across 
the  center  line  and  the  breaker  flies  open.  There  are  no  latches 
or  triggers  to  hold  arm  closed,  merely  the  rollers  which  are  non- 
rustable  and  practically  without  any  wear. 

There  is  an  eccentric  pin  stop  for  the  roller  which  limits  the 
distance  it  passes  over  center.  The  breaker  may  thus  be  made 


66          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

more  or  less  sensitive  as  desired.  This  cut  shows  the  construc- 
tion in  sizes  over  1200  amperes,  in  which  the  laminations  are 
continuous  from  brush  to  bus  bar.  In  other  respects  the  con- 
struction of  smaller  sizes  is  similar. 

The  industrial  type  of  circuit  breaker  is  built  in  capacities 
up  to  100  amperes  for  voltages  up  to  250  D.C.  and  440  A.C. 
They  are  made  either  front  or  rear  connection  and  are  of  simple 
and  rugged  design. 

WESTINGHOUSE  CIRCUIT  BREAKERS 

The  Westinghouse  Electric  &  Manufacturing  Company,  who 
were  one  of  the  first  to  develop  the  Carbon  Circuit  Breaker, 
have  complete  lines  of  breakers  from  the  type  F  that  is  built 
in  capacities  up  to  75  amperes,  250  volts,  up  to  the  largest 
capacity  for  which  there  is  any  demand. 

Type  F. — The  type  F  are  small,  and  compact  single-pole 
carbon  breakers.  They  readily  take  the  place  of  switches  and 
fuses  and  occupy  about  the  same  space  as  a  fuse  block  and  fuse. 
They  are  designed  to  fulfill  a  demand  for  a  protective  device  to 
be  used  with  small  motor  and  lighting  installations,  and  have  a 
cost  commensurate  with  those  of  such  systems. 

The  overload-operating  solenoid  is  inside  a  fibre  tube  form- 
ing the  lever  arm.  The  tripping  point  may  be  set  for  any  current 
within  the  tripping  range  by  a  little  knurled  thumb  screw  located 
below  the  pivot.  A  small  insulating  knob  at  the  right  controls 
the  tripping  device  and  offers  a  means  of  opening  the  breaker  by 
hand. 

The  current-carrying  contacts  are  copper,  the  arcing  con- 
tacts are  carbon  and  are  readily  renewable.  The  lower  arm  is 
operated  by  a  spring  and  the  copper  contacts  are  of  a  shape  to 
assist  in  opening  the  breaker. 

Type  CD. — Type  CD  carbon  circuit  breakers  shown  in  Fig. 
46  are  supplied  for  separate  or  panel  mounting.  These  breakers 
are  supplied  for  voltages  up  to  750  and  for  capacities  up  to 
300  amperes.  They  may  be  used  for  motor  starting-control 
of  industrial  circuits  and  as  feeder  circuit  breakers  in  moderate 
size.  The  main  or  brush  contact  is  made  of  laminated  copper 
having  high-pressure  contact  with  an  excellent  wiping  or  self- 
cleaning  action.  When  the  breaker  is  opened,  the  main  contact 
is  opened  first  and  the  current  is  shunted  upward  through  auxili- 
ary contacts  where  the  circuit  is  broken.  The  secondary  contacts 


CARBON  BREAKERS 


67 


FIG.  46. — Westinghouse  carbon  circuit  breaker,  type  CD. 


FIG.  47. — Westinghouse  circuit  breaker  type  "CC.' 


68 


SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


are  of  flat  phosphor  bronze.  The  arcing  contacts  are  of  carbon 
and  have  a  wiping  action,  making  them  self-aligning  and  self- 
cleaning. 

Type  CC. — The  type  CC  carbon  circuit  breaker  shown  in 
Fig.  47  for  protection  of  alternating-current  and  direct-current 
circuits  of  moderate  capacities  are  supplied  for  voltages  of  750  or 
less  and  for  capacities  up  to  800  amperes.  These  breakers  are 
manually  operated  and  are  closed  by  pulling  down  on  the  operat- 
ing handle,  and  may  be  tripped  manually  by  pushing  upwards 
on  the  handle  or  back  on  the  calibrating  thumb  knob.  In 
closing  a  breaker,  the  brush  is  forced  against  the  contact  plates 
by  means  of  a  toggle-joint  lever.  A  small  steel  roller  engages  a 
locking  catch,  places  the  two  releasing  springs  under  tension, 
and  holds  the  breaker  in  the  closed  position.  Friction  clips,  which 
engage  a  projection  on  the  handle  eliminate  any  destructive 
effects  of  jarring  due  to  the  opening  of  the  breaker. 


FIG.  48. — Westinghouse  carbon  circuit  breaker,  type  CA. 

Contacts. — The  main  contacts  are  made  of  laminated  copper 
brushes  and  attached  to  the  upper  end  of  each  movable  contact 
is  a  phosphor-bronze  secondary  contact  that  bears  on  the  main 
stationary  contact  when  the  breaker  is  closed,  and  opens  after 
the  main  brush  has  entirely  left  the  contact  plate.  By  this 
means,  the  opening  of  the  circuit  is  transferred  from  the  main 


CARBON  BREAKERS 


contacts  and,  in  case  of  any  possible  failure  of  the  carbon  arcing 
contacts,  the  main  contacts  are  protected  from,  the  arc. 

Each  breaker  is  also  provided  with  auxiliary  carbon  arcing 
contacts  which  finally  interrupt  the  circuit,  thereby  preventing 
any  burning  of  the  main  contacts  when  the  breaker  opens.  The 
stationary  carbon  contact  is  securely  fastened  to  the  stud  im- 
mediately above  the  upper  stationary  main  contact.  The  mov- 
able carbon  contact  is  mounted  immediately  above  the  movable 
main  contact  to  which  it  is  connected  by  a  shunt  composed  of 
braided  flexible  copper.  This  contact  is  so  mounted  that  the 
main  and  secondary  contacts  are  open  about  one-quarter  inch 
before  the  carbons  separate,  thus  eliminating  any  possibility 
of  the  metallic  contacts  being  blistered  by  the  arc.  The  movable 
carbon  contact  is  pivoted  on  the  supporting  frame  in  such  a 
manner  that  it  is  in  perfect  alignment  with  the  stationary  contact 
whenever  the  breaker  is  closed.  These  carbon  contacts  are 
inexpensive  and  readily  renewable. 

Type  CA. — Type  CA  carbon  circuit  breakers,  Fig.  48,  are 
designed  particularly  for  the  severe  current-carrying  and  inter- 
rupting conditions  found  in  operating  low  voltage  direct  and 
alternating-current  systems.  They  are  made  in  the  following 
capacities,  based  on  30-degree  Centigrade  rise : 

MAXIMUM  AMPEHES 


For  circuit 

Manually 

Manually 

Max. 

operated 

operated 

Electrically 

Current 

Frequency 
cycles 

volts 

direct 
control 

remote 
control 

operated 

Direct  

(      750 
\  1,500 

24,000 

2,500 

24,000 
8,000 

Alternating  .... 

(28 

750 

10,000 



10,000 

\  60 

750 

7,000 

7,000 

Distant  Control. — When  conditions  make  it  desirable  to 
operate  carbon  circuit  breakers  from  a  distance,  the  electrically 
operated  form  or  the  manually  operated  remote  control,  within 
its  limited  application,  is  furnished.  This  makes  it  possible  to 
install  the  circuit  breaker  near  the  apparatus  to  be  connected, 
like  the  equalizer  connection  of  a  direct-current  generator,  and  to 


70 


SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


retain  the  control  at  the  switchboard.  Another  common  applica- 
tion of  the  electrically  operated  form  is  for  remote-control 
feeder  tie  switches  on  distributing  systems.  Such  arrangements 
effect  a  saving  in  wiring,  as  a  light  control  cable  takes  the  place 
of  the  heavy  power  cable  otherwise  required. 

The  simple  form  of  toggle  mechanism  used  throughout  is 
especially  worthy  of  note.     This  toggle  on  all  sizes,  from  3000 

to  24,000  amperes,  consists  of 
but  a  single  link  member  con- 
necting the  handle  lever  and 
main  contact  arm,  but  is  so 
shaped  and  related  to  the 
lever  members  as  to  form  an 
eccentric  toggle  of  exceptional 
power.  In  the  sizes  below 
3000  amperes  the  toggle  is  of 
the  roller  type,  formed  by 
means  of  a  roller  on  the  inner 
end  of  the  handle  lever  acting 
directly  on  a  plane  surface  on 
the  brush-arm  or  main  con- 
tact lever.  Both  forms  are 
best  adapted  to  the  particular 
sizes  of  breaker  and  form  the 
simplest  mechanism  known  to 
be  used  for  the  purpose.  The 
automatic  overload  tripping 
attachment  is  contained  in  the 
circuit  breaker  and  forms  an 
integral  part  of  it. 

Contacts. — In  larger 
capacities,  where  the  moving 
contact  is  subdivided  in  order 


FIG.  49. — Westinghouse  Type  CA  breaker 
— contact  arrangement. 


to  obtain  a  better  average  distribution  of  contact  pressure,  large 
ventilating  spaces  are  allowed  between  the  individual  laminated 
main  contact  members.  This  reduces  the  temperature  rise  very 
materially  under  any  given  conditions  of  load  and  increases  the 
capacity  on  alternating-current  service  by  reducing  the  "skin 
effect."  When  the  breaker  is  tripped,  the  main  contacts  are 
opened  first  and  the  current  is  shunted  upward  through  copper 
secondary  and  tertiary  contacts  to  the  carbon  arcing  contacts 
where  the  final  break  takes  place.  See  Fig.  49. 


CARBON  BREAKERS  71 

This  shows  the  shape  and  relative  position  of  each  of  the 
contacts  in  the  three  important  stages  of  breaking  the  circuit,  as 
follows : 

1.  Contacts  outlined  by  dotted  lines  show  main  brush  opened, 
secondary  contact  on  point  of  opening  and  tertiary  and  carbon 
contacts  not  changed  from  closed  position. 

2.  Contacts  shown  by  light  shading  show  main  and  secondary 
contacts  open,  tertiary  and  carbon  contacts  still  closed,  but  one 
set  of  contacts  has  slid  down  on  the  other  set. 

3.  Contacts  shown  by  heavy  shading  show  the  tertiary  contact 
open  and  carbon  tips  about  to  finally  break  the  circuit. 

Directly  over  the  brush  contacts  the  secondary  contacts  are 
located.  The  secondary  stationary  contact  has  a  surface  in- 
clined to  the  vertical  and  practically  parallel  to  the  plane  of 
support  of  the  moving  contact  spring,  thus  preventing  buckling 
of  the  spring  in  case  the  contact  is  roughened  by  repeated  opening 
under  short-circuit  conditions.  The  moving  contact  spring  is 
held  under  initial  pressure  until  just  before  the  contacts  separate. 
The  secondary  contacts  open  next  after  the  main  or  brush  con- 
tacts open,  protecting  the  latter  from  arcing  under  severe  short- 
circuit  conditions. 

An  adjusting  screw  on  the  moving  contact  allows  an  adjust- 
ment of  the  relation  of  the  opening  of  the  main  and  secondary 
contacts. 

The  tertiary  contacts  are  attached  to  the  lower  end  of  the 
carbon  contacts  of  which  they  appear  to  be  a  part.  They  are 
made  of  copper  and  are  connected  to  the  main  or  brush  contacts 
by  heavy  copper  shunts.  They  open  immediately  before  the 
carbon  contacts  open  and  fully  protect  the  secondary  contacts 
except  under  extreme  conditions  of  repeated  short  circuit  with- 
out proper  maintenance. 

The  carbon  or  final  contacts,  except  where  exposed  to  the  arc, 
are  heavily  copper  coated  or  filled,  thus  insuring  lowest-resistance 
contact  with  the  tertiary-contact  copper  plates  and  the  shunts  to 
the  main  contacts.  They  are  self-aligning  and  have  a  self- 
wiping  action,  thus  making  them  self-cleaning. 

The  carbon  arms  are  of  ample  length  and  open  far  enough  to 
insure  breaking  the  heaviest  arc  incident  to  short  circuit,  as  in 
heavy  railway  service. 

Contactor  Type. — A  line  of  breakers  known  as  the  type  CA 
contactor-type  circuit  breaker  (see  Fig.  50)  is  available  in  capa- 


72          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


cities  from  1000  amperes  to  8000  amperes  direct-current,  inclu- 
sive, and  in  intermediate  capacities  corresponding  to  the  regular 
type  CA  single-pole  line.  The  term  "contactor  type"  means  a 
breaker  that  is  electrically  operated,  but  held  in  the  closed  posi- 
tion by  the  presence  of  a  small  amount  of  closing  current  on  the 
operating  magnet  and  not  by  a  mechanical  latch,  as  is  usual 
with  the  standard  manually  or  electrically  operated  type  CA 
breakers.  The  breaker  drops  to  the  open  position  on  the  absence 
of  voltage  in  the  control  circuit.  The  contactor  type  of  electri- 
cally operated  breaker  is  much  more  simple 
than  the  standard  electrically  operated  form, 
which  has  all  of  the  parts  of  the  regular  man- 
ually operated  breaker  and  the  electric  operat- 
ing mechanism  in  addition.  However,  they 
are  made  only  in  the  single-pole  non-automatic 
form,  which  accounts  for  part  of  the  simplicity. 
The  contactor  breaker  is  made  automatic 
by  the  addition  of  overload  or  reverse  power 
relays  arranged  to  open  the  closing  coil  circuit 
or  to  short-circuit  the  closing  coil  with  re- 
sistance in  series.  The  latter  relay  scheme 
permits  the  use  of  standard  contact-closing 
relays. 

The  contactor  breaker  is  adapted  for  use 
as  an  automatic  feeder  tie  switch  in  con- 
junction with  appropriate  relays  and  con- 
nections. In  this  service  it  is  adjusted  to 
open  when  the  voltage  drops  below  a  certain  predetermined 
limit,  as  would  be  caused  by  an  excessive  overload  or  short 
circuit  in  the  vicinity.  The  breaker  will  then  remain  open 
until  some  predetermined  voltage  exists  on  both  feeders  that  it 
is  arranged  to  tie,  and  then  automatically  closes. 

Multipole  contactor  breakers  are  made  by  using  several  single- 
pole  units  controlled  by  a  single  control  switch  or  relay  or  both. 
Manually  Operated  Remote -control  Breakers. — For  service 
up  to  1500  volts  direct  current  and  capacities  up  to  2500  am- 
peres, single-pole  type  CA  manually  operated  breakers  are  sup- 
plied for  mounting  above  or  away  from  the  switchboard  panels, 
but  operated  from  a  handle  mounted  on  the  panel  in  the  usual 
location  for  the  knife  switch.  See  Fig.  51. 


FIG.  50. — Westing- 
house  contactor  type 
breaker. 


CARBON  BREAKERS 


73 


FIG.  51. — Westinghouse  remote-control  1500-volt  breaker. 


FIG.  52. — Westinghouse  electrically  operated  breaker. 


74          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Multipole  Circuit  Breakers. — Each  multipole  breaker  is  pro- 
vided with  a  common  trip;  that  is,  an  overload  on  any  one  pole 
trips  all  poles.  The  manually  operated  breakers  (two,  three"or 
four-pole),  up  to  and  including  2500-amperes  capacity  can  be 
provided  with  a  single  closing  handle  and  crossbar  for  closing  all 
poles  together  (all  poles  tripped  together).  This  form  of  handle 
is  arranged,  by  springs,  to  retrieve  independently  of  the  breaker 
pole  units  so  as  not  to  retard  the  operation  of  the  breaker  on 
opening. 

Solenoid  Operated. — The  electrically  operated  multipole 
breakers,  Fig.  52,  are  supplied  in  any  standard  number  of  poles 
and  in  any  standard  ampere  capacity  in  which  the  type  CA 
line  is  listed.  They  have  a  common  electromagnet  for  closing 
all  poles  and  a  single  shunt-trip  magnet  acting  through  a  common 
trip  mechanism  for  tripping  all  poles  of  the  breaker  together. 

Direct-current  shunt-trip  attachments  arranged  for  mounting 
on  the  front  of  the  panel  are  made  for  all  capacities  of  manually 
operated  type  CA  breakers. 

A  direct-current  automatic  undervoltage-trip  attachment  is 
made  for  the  several  capacities  of  type  CA  breaker.  This 
attachment  is  reset  automatically  by  the  opening  of  the  circuit 
breaker. 

An  inverse  time  limit  dashpot  with  an  adjustable  time  feature 
is  made  for  all  sizes  of  CA  breakers  up  to  and  including  2500 
amperes  direct  current  and  1600  amperes  alternating  current, 
in  any  number  of  poles  up  to  four  poles,  and  for  both  manually 
and  electrically  operated  breakers.  A  similar  attachment  for 
the  larger  capacity  breakers  can  be  supplied. 

An  attachment  for  tripping  the  type  CA  carbon  circuit 
breaker  on  reversal  of  current  in  direct-current  service  is  made  to 
be  applied  to  any  regular  type  CA  carbon  circuit  breakers  of 
capacities  up  to  20,000  amperes. 


CHAPTER  IV 
OIL  CIRCUIT  BREAKERS 

Application. — It  is  generally  conceded  that  for  opening  large 
amounts  of  alternating-current  power  and  for  controlling  all 
alternating-current  high  voltage  circuits  nothing  at  the  present 
time  is  superior  to  oil  circuit  breakers.  There  are  three  funda- 
mental reasons  for  this :  First,  the  fact  that  this  type  of  breaker 
terminates  the  alternating-current  wave  at  its  normal  zero  value, 
eliminating  excessive  surges  in  the  connected  circuits;  second, 
the  compactness  of  form  of  the  apparatus;  and  third,  the  fact 
that  this  type  of  apparatus  properly  designed  reduces  the  fire 
and  life  hazards  to  a  minimum. 

When  an  oil  circuit  breaker  is  opened  under  load,  an  arc  is 
formed  between  the  stationary  and  the  moving  contacts,  the 
size  of  the  arc  depending  upon  the  voltage,  the  amount  of  current, 
and  rate  of  contact  separation.  The  heat  of  the  arc  disintegrates 
some  portion  of  the  arcing  contacts  and  some  of  the  oil  surround- 
ing the  contacts,  forming  a  gas  bubble  of  a  size  that  depends  on 
the  amount  of  current  flowing  and  on  the  duration  of  the  arc. 
If  this  gas  bubble  is  immediately  carried  away  from  the  con- 
tacts and  the  contacts  have  been  sufficiently  separated,  the  arc 
will  persist  only  until  the  next  zero  of  the  current  wave.  The 
ability  of  the  bubble  to  rise  away  from  the  contacts  depends 
upon  the  relative  specific  gravity  of  the  gas  and  oil,  and  the 
head,  volume,  and  viscosity  of  the  oil.  Oil  having  high  specific 
gravity  and  sufficient  head  will  exert  pressure  enough  to  force 
the  bubble  up  and  away  from  the  contacts,  irrespective  of  their 
position. 

Features. — The  following  features  apply  to  practically  all 
high-grade  American  oil-circuit  breakers  of  any  make,  and  are 
generally  recognized  as  embodying  the  best  practice. 

These  are:  open  position  maintained  by  gravity,  so  that  the 
contacts  fall  to  open  position  in  case  of  injury  to  the  moving 
contacts  or  the  lifting  rods;  the  rapid  acceleration  of  the  moving 
parts  on  opening  to  minimize  the  duration  of  arcing,  the  tank 

75 


76          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

pressure,  and  the  deterioration  of  the  arcing  contacts;  all  live 
parts  immersed  under  a  deep  head  of  oil  to  absorb  the  shock  of 
short  circuits  and  to  prevent  the  excessive  development  of  gases 
when  rupturing  large  amounts  of  power;  proper  venting  and 
baffling  arrangements  for  oil  tanks  to  provide  regulated  escape 
for  the  gases  formed  by  rupturing  heavy  overloads  and  short 
circuits;  sturdy  mechanical  construction  throughout;  isolation  of 
individual  poles  in  insulated  cells  on  moderate  voltage  service, 
and  in  separate  tanks  on  high  voltage;  use  of  generously  pro- 
portioned high-pressure  wiping  and  self -cleaning  contacts;  pro- 
tection of  the  main  contacts  by  arcing  contacts  so  located  that 
the  main  current  exerts  a  blowout  effect  on  the  arcs;  use  of 
electric  solenoid  for  electric  operation  and  the  use  of  full-auto- 
matic design  of  latching  devices,  preventing  the  possibility  of 
holding  the  contacts  in  the  closed  position  when  heavy  over- 
loads and  short  circuits  exist  on  the  line. 

The  type  H-3,  H-6,  and  H-9  breakers  of  the  General  Electric 
Company  form  a  notable  exception  to  some  of  the  features 
described  above  as  their  moving  contacts  are  downward  closing, 
motor  operated,  but  they  embody  many  of  the  other  features 
and  have  been  remarkably  successful  in  their  actual  performance. 

Rating. — The  selection  of  an  oil  circuit  breaker  for  application 
to  an  electrical  system  or  circuit  requires  a  knowledge  of  the 
characteristics  of  the  breaker  and  the  characteristics  of  the 
system  or  circuit.  Breakers  are  usually  classified  according  to 
their  rated  voltage,  rated  current,  rated  frequency,  interrupting 
capacity  and  instantaneous  current  capacity.  Systems  may  be 
classified  according  to  their  normal  operating  voltage,  normal 
current,  normal  frequency,  and  current  transients. 

The  rated  voltage  of  a  breaker  is  the  greatest  normal 
voltage  as  read  by  voltmeter  in  volts  between  any  two  wires 
of  any  circuit  to  which  the  breaker  should  be  connected. 
When  referred  to  the  breaker,  it  is  a  function  of  its  insulation 
strength  and  of  the  safety  factor  desired.  The  American  Institute 
of  Electrical  Engineers  has  established  standards  for  the  insula- 
tion strength  of  oil  circuit  breakers.  All  high-grade  indoor 
oil  breakers  are  tested  at  2%  times  rated  voltage  plus  2000 
volts,  and  all  outdoor  oil  breakers  will  stand  the  wet  test  of  twice 
rated  voltage  plus  1000  volts  as  specified  in  these  rules. 

Altitude. — Standard  ratings  of  oil  breakers  are  good  for 
altitudes  of  3300  feet  above  sea  level  and  less.  For  higher 


OIL  CIRCUIT  BREAKERS  77 

altitudes,  standard  breakers  must  be  used  on  voltages  less  than 
rated  voltage,  the  amount  of  derating  depending  on  the  altitude. 
For  operation  above  3300  feet  the  voltage  ratings  given  must  be 
multiplied  by  the  following  factors: 

Distance  above  Voltage  rating  factor 

sea  level,  feet  (G.E.  Co.) 

4,000  .874 

6,000  .825 

8,000  .775 

10,000  .728 

12,000  .684 

14,000  .64 

For  applications  at  high  altitudes,  circuit  breakers  equipped 
with  special  terminals  can  be  supplied  as  special  and  should  be 
taken  up  with  the  manufacturing  company. 

The  normal  operating  pressure  of  a  system  is  the  greatest 
pressure  in  volts  ordinarily  maintained  between  any  two  con- 
ductors. 

Rated  Current. — The  rated  current  of  a  breaker  is  the  greatest 
current  in  amperes  which  it  will  carry  continuously  at  a  specified 
frequency  without  any  essential  part  having  its  temperature 
raised  more  than  a  specified  number  of  degrees  above  an  ambient 
temperature,  or  above  a  fixed  temperature.  The  American  Insti- 
tute of  Electrical  Engineers  has  established  heating  standards 
for  oil  circuit  breakers.  They  limit  the  maximum  permissible 
temperature  rise  of  coils  and  insulating  materials  of  oil  circuit 
breakers  65  degrees  Centigrade  based  on  an  ambient  temperature 
of  40  degrees  Centigrade,  and  the  rise  of  other  parts  whose 
temperature  does  not  affect  the  temperature  of  the  insulating 
material  to  be  such  as  not  to  be  injurious  in  other  respects. 
They  also  limit  the  maximum  temperature  of  oil  and  contacts  in 
oil  to  70  degrees  Centigrade.  For  an  ambient  temperature  of  40 
degrees  Centigrade,  this  permits  a  temperature  rise  of  30  degrees 
Centigrade  for  oil  and  contacts  in  oil.  Where,  however,  the 
ambient  temperature  is  less  than  40  degrees  Centigrade,  ad- 
vantage may  be  taken  of  the  condition  to  operate  the  parts  at 
a  higher  temperature  rise  if  the  maximum  temperatures  specified 
are  not  exceeded. 

Inasmuch  as  a  circuit  breaker  reaches  its  final  temperature 
quickly  with  steady  current  load,  it  is  necessarily  a  maximum 
rated  device.  On  25-cycle  service  a  circuit  breaker  above  300 


78          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

amperes  rating  will  carry,  continuously,  considerably  more  than 
its  60-cycle  rating,  and  25-cycle  current  ratings  are  therefore 
given  on  600  ampere  breakers  and  above. 

Interrupting  Capacity. — The  interrupting  capacity  of  an  oil 
circuit  breaker  is  the  highest  current  in  amperes  which  it  will 
interrupt  at  any  specified  normal  pressure,  frequency  and  duty. 
This  conforms  with  the  standards  adopted  by  the  American 
Institute  of  Electrical  Engineers. 

The  duty  on  which  the  ampere  tables  have  been  based  assumes 
that  the  breaker  will  interrupt  a  circuit  two  times  at  a  2-minute 
interval  and  then  be  in  condition  to  be  closed  and  carry  its  rated 
current  until  it  is  practicable  to  inspect  it  and  make  any  neces- 
sary readjustments.  This  definition  of  interrupting  capacity 
selects  the  most  common  condition  of  oil  circuit-breaker 
operation. 

The  duty  performed  by  a  circuit  breaker  in  interrupting  the 
current  at  a  given  voltage  is  dependent  upon  the  current  volume 
and  is  a  maximum  for  the  largest  current.  Similarly,  the  duty 
at  varying  voltages  for  a  given  current  is  increasingly  more  diffi- 
cult at  higher  voltages.  A  given  breaker  equipment  for  any 
voltage — within  its  rating  and  under  proper  normal  adjustment — 
has  a  certain  maximum  current  interrupting  ability.  It  should 
not  be  applied  to  a  service  demanding  interrupting  capacity 
beyond  this  ability. 

Rating. — The  proper  method  of  rating  breakers  was  long  a 
debatable  question  and  caused  a  considerable  amount  of  mis- 
understanding when  comparing  various  breakers. 

A.  I.  E.  E.,  1916.— In  the  September,  1916,  Proceedings  of  the 
A.  I.  E.  E.  there  were  two  papers  presented,  one  by  Mr.  E.  M. 
Hewlett,  of  the  General  Electric  Company,  and  the  other  by  Mr. 
S.  Q.  Hayes  of  the  Westinghouse  Electric  &  Manufacturing  Com- 
pany, on  this  subject  of  circuit-breaker  ratings,  and  these  papers 
with  the  resulting  discussions  did  a  good  deal  to  pave  the  way 
for  a  more  definite  method  of  rating  circuit-breaker  rupturing 
capacities. 

A.  I.  E.  E.,  1918.— A  later  meeting  of  the  A.  I.  E.  E.  in  Feb- 
ruary, 1918,  was  devoted  to  the  consideration  of  a  paper  prepared 
jointly  by  Mr.  G.  A.  Burnham,  of  the  Condit  Electrical  Manu- 
facturing Company,  Mr.  E.  M.  Hewlett,  of  the  General  Electric 
Company,  and  Mr.  J.  N.  Mahoney,  of  the  Westinghouse  Electric 
&  Manufacturing  Company.  This  paper  contained  a  great  deal  of 


OIL  CIRCUIT  BREAKERS 


79 


Short-Circuit  Characteristics  For  Jhree-Pha.se  Systems. 
Based  on  Total  Kva.  Rating  of  Synchronous  Machines. 


RMS.  Current  in  Terms  of 

Total  FulkLoad  Current  of  Machines, 

Initial  Full  Load  at  a  Power  Factor  of  80%  Assumed 


Q     02.    0.4    0.6    O.B    ID     Li     14    1.6     1.6    2.0    22     2.4     ZB    2&    3JO 
FIG.  53. — Short  circuit  characteristics — 30  per  cent,  reactance  or  less. 


Short-Circuit  Charateristics  For  Threefhase  Systems: 
Based  on  Total  Kva.  Rating  of  Synchronous  Machines. 


RMS.  Current  inTermsor 
Total-Full  Load  Current  of  Machines, 
Initial  Full  Load  at  a  Power  Factor  of  80  %  Assumed 


JO      OZ    0.4    0£     0.8     1.0    J2     U     I.G     1.8    20     2.2     2.4    2£-2J     3JO 
FIG.  54. — Short  circuit  characteristics — 40  per  cent,  reactance  or  more. 


80          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

valuable  data  in  the  form  of  curves  of  the  short-circuit  condi- 
tions to  be  met  with  in  the  average  plants  of  different  reactances 
at  the  expiration  of  different  lengths  of  time.  These  curves 
were  based  on  an  average  of  a  large  number  of  curves  of  actual 
modern  generators  built  by  the  General  Electric  Company  and 
the  Westinghouse  Electric  &  Manufacturing  Company,  and  can 
be  taken  as  representative  of  present  American  Generator 
Design. 

Short-circuit  Curves. — These  curves  slightly  modified  for 
convenience  are  reproduced  in  Figs.  53  and  54  and  they  show 
very  clearly  how  the  short-circuit  values  die  down  very  rapidly 
after  a  small  fraction  of  a  second,  and  how  the  reactance  of  the 
system  has  a  great  deal  to  do  with  these  values. 

The  characteristic  shapes  of  the  time  current  decrement  curves 
have  been  arrived  at  by  analysis  of  alternator  tests  including 
oscillograph  studies  of  short  circuits  occurring  when  the  alter- 
nators were  excited  to  full  voltage  and  were  carrying  various 
loads  at  various  power  factors. 

In  the  curves  for  total  reactances  up  to  and  including  20  per 
cent.,  the  reactance  is  assumed  to  be  wholly  within  the  alternator 
and  for  higher  values  of  reactance  the  alternators  were  taken  at 
20  per  cent,  and  due  allowance  made  by  calculation  for  the  effect 
of  the  external  reactances. 

The  final  values  of  the  current,  i.e.,  the  sustained  short-circuit 
current,  have  been  assumed  in  accordance  with  experience  and 
tests  and  are  based  on  the  behavior  of  machines  of  normal  design. 

The  percentage  reactance  in  any  leg  of  a  circuit  is  the  reactance 
drop  in  that  leg  of  the  circuit  at  normal  current  expressed  as  a 
percentage  of  the  voltage  to  the  neutral  of  that  circuit.  The 
percentage  values  are  initial  values  based  on  a  symmetrical  sine 
wave  and  on  the  maximum  rating  of  the  machines  connected  to 
the  bus.  The  percentage  of  reactance  of  alternators  varies  from 
about  8  per  cent,  to  30  per  cent.  The  percentage  reactance  of 
transformers  varies  from  about  3  per  cent,  to  30  per  cent. 

Breaker  Application. — The  problem  of  breaker  application 
after  the  service  voltage  has  been  fixed  is  to  determine  the  maxi- 
mum current  that  may  be  encountered,  and  then  the  breaker 
should  be  chosen  with  an  interrupting  capacity  equal  to  or  greater 
than  this  maximum  current. 

Various  formulae  for  determining  the  increased  rupturing 
capacity  to  be  assigned  to  a  breaker  when  it  is  used  at  less  than 


OIL  CIRCUIT  BREAKERS  81 

its  rated  voltage  have  been  offered  but  it  is  usual  to  convert  the 
current  rating  into  a  K.V.A.  rating  at  the  listed  voltage  and  then 
allow  an  increase  in  K.V.A.  rating  as  the  voltage  is  lowered. 

The  generally  accepted  method  of  rating  is  to  estimate  an 
increase  in  K.V.A.  rating  of  73^  per  cent,  at  75  per  cent,  of  listed 
voltage,  an  increase  of  15  per  cent,  at  50  per  cent,  of  listed  voltage 
and  an  increase  of  22^  per  cent,  at  25  per  cent,  of  listed  voltage, 
all  of  these  figures  being  contingent  on  the  fact  that  the  current 
calculated  on  this  basis  did  not  exceed  a  definite  figure,  deter- 
mined experimentally,  that  expressed  the  maximum  current 
that  the  breaker  contacts  could  pass  for  1  second  or  5  seconds 
without  danger  of  welding  the  contacts  or  causing  mechanical 
distortion  due  to  magnetic  forces.  While  these  figures  differ 
somewhat  with  the  details  of  design,  they  are  usually  given  as 
50  times  normal  for  5  seconds  and  in  a  few  cases  as  100  times 
normal  for  1  second. 

The  rating  of  a  circuit  breaker  in  current  interrupted  at  normal 
operating  pressure  simplifies  the  selection  of  a  proper  breaker  for  a 
given  service  condition. 

Time  of  Tripping. — The  time  delay  of  oil  circuit-breaker 
mechanisms  has  an  appreciable  effect  upon  the  current  which 
they  will  be  called  upon  to  interrupt  under  transient  conditions. 
The  contacts  of  ordinary  oil  circuit  breakers  part  in  from  0.05  to 
0.40  seconds  after  the  tripping  circuit  is  energized,  depending 
on  the  kind  of  operating  mechanism  and  tripping  methods  used. 

The  data  given  for  the  selection  of  oil  circuit  breakers  is 
applicable  only  to  average  systems.  Therefore,  a  short  dis- 
cussion of  other  factors  requiring  separate  or  more  detailed  atten- 
tion seems  worth  while. 

Effect  of  Regulators. — When  the  alternators  are  equipped  with 
automatic  voltage  regulators  such  regulators  will  increase  the 
excitation  after  a  short  circuit  in  the  endeavor  to  hold  normal 
voltage  on  the  bus  bars.  The  maximum  voltage  which  can  be 
obtained  from  the  exciters  will  be  ordinarily  not  more  than  50 
per  cent,  greater  than  that  required  at  full  load  80  per  cent, 
power  factor  on  the  alternators.  Under  short  circuit,  the  alter- 
nator terminal  voltage  is  reduced,  hence  the  resultant  flux  density 
in  the  alternator  iron  is  also  reduced.  A  given  increase  in 
excitation,  therefore,  produces  a  proportionate  increase  in  cur- 
rent flowing  in  the  short  circuit.  Hence,  as  can  be  assumed,  the 
excitation  is  increased  50  per  cent.,  the  sustained  short-circuit 


82         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


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Method  of  tripping  breaker  corresponding 
to  time  elapsed 

No  relay  A.C.  series  trip  coil  
Cur.  trans,  with  A.C.  trip  coil.  .  . 

Solenoid  or  motor  relay  Cur.  trans,  with  A.C.  trip  coil.  .  .  . 
Cur.  trans,  with  D.C.  trip  coil  

Induction  relay  Cur.  trans,  with  A.C.  trip  coil  .  .  . 
Cur.  trans,  with  D.C.  trip  coil.  .  .  . 

Circuit  breakers  having  A.C.  or  D.C.  trip  with  definite 
time  setting. 

OIL  CIRCUIT  BREAKERS  83 

current  will  be  approximately  50  per  cent,  greater  than  the 
sustained  current  due  to  full-load  80  per  cent,  power  factor 
excitation. 

An  appreciable  time,  however,  is  required  for  the  excitation 
to  increase  to  its  maximum  value.  During  the  first  half-second 
the  amount  of  short-circuit  current  is  not  affected  by  the  presence 
of  the  voltage  regulator  but  from  this  time  on  the  current  curve 
is  higher,  reaching  the  value  at  the  end  of  2  or  3  seconds 
of  50  per  cent,  greater  than  the  current  without  the  regulator. 

An  exception  to  the  above  appears  when  the  external  reactance 
is  so  high  and  the  short-circuit  current  so  limited  that  the  regula- 
tor is  able  to  maintain  normal  voltage  at  the  generator  terminals. 
In  such  cases  the  sustained  current  will  be  limited  to  the  current 
which  will  pass  through  the  external  reactance  with  normal 
voltage  impressed  upon  it. 

Automatic  Recommendations. — These  are  based  on  the  as- 
sumptions that  the  breaker  is  in  good  operating  condition  and 
that  its  contacts  will  not  part  in  less  than  the  listed  maximum 
time  after  the  maximum  instantaneous  value  of  the  abnormal 
current  has  been  reached.  Any  faulty  condition  of  the  breaker, 
such  as  poor  oil,  stiff  bearings,  sluggish  operation,  or  accumula- 
tion of  dust  will  diminish  its  interrupting  capacity.  Also,  if  the 
contacts  part  in  a  shorter  time  than  the  listed  minimum,  a 
larger  breaker  will  be  required,  while  if  the  contacts  part  after 
a  greater  time  than  the  listed  minimum  values,  a  smaller  breaker 
may  be  used. 

Time  Relays. — These  may  be  used  to  delay  the  parting  of  the 
oil  circuit-breaker  contacts  after  the  start  of  the  abnormal  cur- 
rent. The  greater  the  delay,  the  less,  in  general,  will  be  the 
current  to  be  interrupted.  Hence  by  inserting  a  time  delay 
relay,  suitably  adjusted,  a  given  automatic  oil  circuit  breaker 
may  be  used  on  a  larger  system,  or  for  a  given  system,  a  smaller 
breaker  may  be  used. 

Short  circuits  in  cables  are  not  instantaneous  in  nature  but 
develop  gradually  into  dead  short  circuits.  On  such  a  short, 
a  current  may  pass  sufficient  to  actuate  the  breaker  relay  and 
develop  into  a  dead  short  circuit  at  the  time  the  breaker  con- 
tacts open.  Where  full  protection  is  required  for  such  cases,  a 
breaker  good  for  the  initial  value  of  short-circuit  current  must  be 
used. 


84          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Manufacturers'  Guarantees. — The  rupturing  capacities  as- 
signed by  manufacturers  to  their  breakers  are  modified  from  time 
to  time  due  to  improvements  in  design,  changes  in  materials 
employed  and  methods  of  manufacture  used,  but  those  given  in 
this  book  are  those  that  were  considered  correct  by  the  manu- 
facturers at  the  time  of  publication.  These  are,  of  course,  sub- 
ject to  change  by  the  manufacturers. 

Direct  Control. — The  earliest  electrical  power  plants  containing 
a  few  machines  of  small  output  and  moderate  voltage  were 
easily  controlled  from  switchboards  where  all  of  the  switches, 
meters,  etc.,  were  placed  on  panels.  As  voltage  and  output 
increased  it  became  necessary  to  utilize  more  space  for  the  switch- 
ing devices  and  to  operate  them  either  by  compressed  air  or  by 
mechanical  or  electrical  means  from  a  central  point. 

Distant  Control. — For  the  distant  mechanical  operation  of 
oil  circuit  breakers  American  practice,  with  its  oil  switches 
usually  designed  for  an  up-and-down  motion,  favors  the  use  of 
bell  cranks  and  rods,  the  latter  ordinarily  being  a  piece  of  standard 
gas  pipe  screwed  into  suitable  terminals  attached  to  the  bell 
cranks,  operating  handles,  etc.  As  far  as  possible  the  different 
portions  of  the  mechanical  transmission  are  arranged  in  tension 
for  closing  the  breaker  to  avoid  bending  stresses,  although  a 
reasonable  amount  of  compression  can  be  taken  care  of  without 
unduly  increasing  the  weight  of  the  mechanism. 

Manual  Operation. — Manual  closing  from  a  cover  plate  lever 
or  handle  on  a  panel  or  frame  bracket  is  the  ordinary  method  of 
closing  small  or  medium  sized  circuit  breakers  both  panel  mount- 
ing and  remote  control.  With  very  large  circuit  breakers 
manual  operation  becomes  impossible  or  undesirable,  owing  to  the 
inability  of  a  man  to  throw  a  large  breaker  fast  enough  for  syn- 
chronizing purposes,  or  even  to  close  the  circuit  breakers  at  all 
without  excessive  mechanical  leverage,  which  is  wasteful  of 
space.  Stresses  in  manually  operated  remote-control  parts 
and  the  mechanical  complication  necessary  to  connect  breakers 
located  in  positions  inaccessible  from  the  switchboard  or  con- 
trol position,  often  preclude  the  use  of  manually  operated 
remote  control. 

In  the  smaller  sizes  of  manually  operated  remote-control 
circuit  breakers,  the  automatic  details  are  mounted  directly 
in  the  cover  plate,  while  in  larger  sizes  the  automatic  latching 
details  are  located  in  a  special  operating  mechanism  mounted  at 


OIL  CIRCUIT  BREAKERS  85 

the  circuit  breaker,  thus  taking  the  strain  of  the  latch  load  off  the 
panel  and  remote-control  bell  cranks  and  levers. 

Where  distance  between  switchboards  and  switching  devices 
makes  the  application  of  hand  operated  breakers  questionable, 
electrically  operated  breakers  should  be  supplied. 

Electric  Control. — Most  of  this  apparatus  now  in  service  is 
designed  for  use  on  a  125-volt  direct-current  circuit,  although 
250,  500  or  any  other  available  direct-current  voltage  can  be 
used.  In  generating  stations  the  exciter  bus  is  sometimes  the 
source  of  the  direct-current  supply,  but  where  a  voltage  regulator 
is  employed  that  causes  the  voltage  of  this  exciter  bus  to  fluctuate, 
it  is  often  advisable  to  install  a  small  storage  battery  in  order  to 
have  a  constant  operating  voltage.  This  battery  is  usually 
charged  from  one  of  the  exciters,  a  small  motor-generator  set, 
or  by  using  suitable  resistances  in  series  with  a  trolley  circuit  or 
other  direct-current  circuit. 

Where,  for  any  reason,  it  is  not  desired  to  install  a  battery  and 
it  is  necessary  to  operate  the  devices  from  an  exciter  bus  with 
fluctuating  voltage,  the  solenoids  or  motors  can  be  designed  so 
that  the  variation  in  voltage  will  not  materially  change  the  pull 
of  the  solenoid  or  the  speed  of  the  motor. 

In  substations  for  D.C.  service,  the  breakers,  etc.,  are  often  de- 
signed for  operation  from  the  direct-current  bus,  and  if  the  station 
has  been  completely  shut  down  and  no  direct  current  is  available, 
the  first  one  or  two  breakers  must  be  closed  by  hand.  A  small 
battery  can  often  be  used  to  advantage  in  such  a  station  and  it 
can  be  charged  through  a  resistance  from  the  D.C.  bus.  In 
transformer  substations  a  small  battery  charged  from  a  motor- 
generator  set  of  about  5  K.W.  capacity  is  nearly  always  installed. 

A.C.  Control. — From  time  to  time  it  has  been  proposed  to 
operate  the  various  devices  from  alternating-current  circuits, 
but  the  direct-current  operation  is  so  much  cheaper  and  the 
additional  complication  due  to  its  use  is  so  small  that  alternating- 
current  operation  has  made  very  little  headway. 

Indicators. — With  any  system  of  distant  control  apparatus,  it 
is  necessary  for  the  operator  to  know  whether  the  different  pieces 
of  apparatus  have  actually  closed  or  opened  or  performed  the 
function  assigned  to  them.  With  manual  operation  the  auto- 
matic opening  of  a  breaker  sometimes  operates  all  of  the  mechan- 
ism back  to  the  handle,  so  no  other  indication  is  needed,  but  in 
other  cases  the  latch  or  toggle  joint  is  at  the  breaker  and  the 


86          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

position  of  the  handle  gives  no  clue  to  the  position  of  the  breaker. 
For  such  cases  or  where  an  auxiliary  source  of  power  is  used  for 
operating  the  devices  some  very  ingenious  methods  of  signalling 
have  been  designed.  For  a  breaker  of  any  sort  a  mechanically 
operated  switch  is  usually  provided  and  this  switch  is  thrown 
from  one  position  to  the  other  by  the  movement  of  some  part  of 
the  mechanism  of  the  main  breaker.  A  certain  amount  of 
lost  motion  is  usually  provided  so  that  unless  the  breaker  goes 
all  of  the  way  in  or  out  the  position  of  the  signal  switch  is  not 
altered.  From  these  signal  switches  circuits  are  run  back  to  the 
switchboard  to  operate  signal  lamps  or  similar  devices.  These 
lamps  are  often  arranged  to  form  part  of  a  miniature  bus  circuit 
to  show  the  connections  that  have  been  made  by  the  breakers. 

In  the  field  of  power  operated  oil  circuit  breakers  other  than 
the  'H'  line  of  G.E.  oil  breakers,  electrical-solenoid  method  of 
closing  is  now  used  almost  universally  to  the  exclusion  of  various 
other  methods,  such  as  motor,  hydraulic,  and  pneumatic  power. 
The  electric-solenoid  type  of  operation  is  very  flexible  and  permits 
mounting  the  operating  mechanism  on  cell  walls,  or  pipe  frames, 
or  on  the  floor  above  or  below,  or  behind  the  circuit  breaker. 

Electric  operating  mechanisms  arfe  usually  provided  with 
combined  accelerating  and  dashpot  attachments,  the  former  to 
insure  speedy  opening  of  the  contacts  on  tripping,  the  latter 
to  dissipate  the  kinetic  energy  of  moving  parts  on  the  end  of  the 
opening  stroke.  They  are  also  usually  equipped  with  dashpots 
under  the  closing  cores  to  absorb  shocks  of  moving  parts  in 
closing.  The  action  of  these  dashpots  is  regulated  by  adjusting 
screws,  which  determine  the  extent  of  the  valve  opening. 

Control  Circuit. — Standard  electric  operating  (closing  and 
tripping)  mechanisms  are  made  for  direct-current  operation. 
This  form,  besides  utilizing  simpler  construction,  being  more 
reliable  in  operation,  and  more  easily  kept  in  repair,  is  much  more 
economical  of  space  and  power  than  alternating-current  mechan- 
isms. For  special  applications,  such  as  for  alternating-current 
electrically  operated  railway  sectionalizing  circuit  breakers  and 
other  installations  where  no  auxiliary  source  of  direct-current 
power  is  available,  special  alternating-current  operating  mechan- 
isms can  be  supplied. 

Mechanism. — The  standard  electric  mechanism  closes  the 
breaker  by  a  direct-current  magnet  and  holds  it  closed  by  a 
latch  and  trigger  or  a  toggle,  which  engage  automatically.  The 


OIL  CIRCUIT  BREAKERS  87 

tripping  mechanism  consists  of  a  direct-current  trip  magnet 
acting  on  a  trigger  which  releases  the  latch,  permitting  the 
breaker  to  open. 

The  closing  and  tripping  mechanism  is  operated  by  a  control 
switch,  with  or  without  control  relays  (switches)  in  the  closing 
circuit,  and  usually  with  signal  lamps. 

All  electric  operating  mechanisms  have  a  small  double-throw 
switch  to  open  the  shunt-trip  coil  circuit  when  the  circuit  breaker 
opens  and  to  operate  the  signal  lamps. 

Control  Voltage. — The  standard  electric  mechanisms  are 
regularly  supplied  with  closing  solenoids  wound  for  70  to  140 
volts  (110  volts  nominal)  direct  current.  The  time  required  to 
close  a  breaker  from  the  time  of  the  closing  of  the  control  switch 
contacts  until  the  arcing  contacts  in  the  breaker  touch,  is  %o 
to  %  o  seconds.  Coils  for  other  than  the  aforementioned  stand- 
ard voltages,  or  of  greater  operating  range,  can  be  supplied. 

The  electric  mechanisms  are  equipped  with  tripping  as  stand- 
ard, to  operate  at  from  50  to  140  volts  direct  current. 

Electric  operating  mechanisms  can  be  furnished  with  closing 
coils  to  operate  at  from  140  to  280  volts,  direct  current,  or  to 
trip  at  from  100  to  280  volts,  direct  current. 

Acceleration. — One  of  the  prime  necessities  in  oil  circuit- 
breaker  operation  is  that  when  the  contacts  have  commenced  to 
separate  they  shall  travel  rapidly,  especially  during  the  first  part 
of  the  stroke.  Speed  of  operation  reduces  the  duration  of  the 
arc,  reduces  the  amount  of  energy  expended  in  the  arc,  reduces  the 
volatilization  of  metal  parts  and  oil,  and,  consequently,  reduces 
the  tank  pressure  which  is  a  determining  factor  in  the  ultimate 
capacity  rating  of  a  breaker.  All  small  automatic  circuit 
breakers  are  provided  with  accelerating  springs  in  the  contacts 
themselves,  which  insures  speedy  operation  when  the  switch 
is  unlatched.  Automatic  overload-trip  remote-control  circuit 
breakers  in  smaller  sizes  are  provided  with  accelerating  devices 
mounted  on  one  of  the  remote-control  bell  cranks.  This  device 
precludes  any  possibility  of  the  sticking  of  the  circuit  breakers, 
when  tripped,  in  case  the  system  of  remote-control  rods  and 
cranks  is  arranged  so  that  they  over  balance  the  weight  of  the 
circuit  breaker  contacts;  it  also  insures  a  rate  of  acceleration  of 
moving  parts  greater  than  that  due  to  unassisted  gravity. 
Where  the  weight  of  the  moving  contact  parts  is  large  and 
there  would  be  danger  of  breakage  if  they  were  suddenly  ar- 


88          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

rested,   the   device  is    equipped    with  means  of  stopping  the 
moving  contact. 

The  beneficial  effect  on  the  operation  of  a  circuit  breaker 
by  this  accelerating  device  is  such  that  a  remote-control  circuit 
breaker  often  can  be  rated  at  a  higher  breaking  capacity  than 
the  corresponding  panel  mounting  circuit  breaker. 

METHODS  OF  TRIPPING 

Non-automatic  Trip. — Manually  operated  circuit  breakers, 
supplied  for  non-automatic  operation,  are  tripped  by  hand  from 
the  faceplate  or  breaker  mechanism.  Electrically  operated 
circuit  breakers  supplied  for  non-automatic  operation  are  sup- 
plied with  a  direct-current  shunt-tripping  magnet  acting  on  a 
trigger  that  releases  the  latch.  The  shunt-tripping  magnet  is 
usually  energized  by  a  circuit  controlled  from  some  central  point, 
or  it  may  be  connected  to  a  relay  circuit,  thus  giving  automatic 
features  through  the  relays. 

When  direct  current  is  not  available  for  operating  the  standard 
shunt  tripping  magnet,  special  magnets  can  usually  be  supplied 
for  using  alternating  current. 

Automatic  Overload  Trip. — Plain-automatic  overload-trip  cir- 
cuit breakers  when  closed  with  an  overload  on  the  line  will  remain 
closed  as  long  as  the  closing  coil  (of  electrically  operated  breakers) 
is  energized,  or  the  manually  operated  mechanism  is  held  in  the 
closed  position.  With  electrically  operated  breakers,  when  the 
closing  coil  circuit  is  opened,  the  breaker  will  not  remain  closed 
on  overloads.  Electrically  operated  circuit  breakers,  only,  are 
regularly  supplied  plain  automatic. 

Full  Automatic. — Full-automatic  overload-trip  circuit  breakers 
have  a  mechanism  making  it  impossible  to  hold  the  breaker  in  a 
closed  position  while  a  continuous  overload  condition  or  short 
circuit  exists  on  the  circuit. 

Transformer  Trip. — For  manually  operated  circuit  breakers 
direct  tripping  from  the  secondary  of  current  transformers  is  the 
most  common  method  of  automatic  overload  tripping  where  no 
time  element  feature  is  necessary.  For  some  low  voltage  indoor 
circuit  breakers,  series  trip  overload  coils  can  be  used,  mounted 
directly  on  the  circuit  breaker. 

Where  time  limit  features  are  wanted,  inverse  time  limit  dash- 
pots  are  supplied  on  some  types  of  circuit  breakers,  or  relays 
having  this  feature  may  be  used. 


OIL  CIRCUIT  BREAKERS  89 

For  electrically  operated  circuit  breakers,  tripping  from  the 
secondary  of  current  transformers  is  most  common.  This 
tripping  can  be  accomplished  by  connecting  the  secondaries 
directly  to  the  current  trip  coils  of  the  circuit  breaker,  or  by  con- 
necting them  to  relays  which  operate  the  current  trip  coils  or 
shunt-trip  coils.  Series  automatic  overload-trip  coils  can  also  be 
used  on  some  electrically  operated  circuit  breakers. 

The  coils  for  current  transformer  automatic  overload  trip  are 
mounted  in  the  cover  plate  or  on  the  breaker  mechanism  of  the 
manually  operated  circuit  breakers,  and  on  the  operating  mechan- 
ism of  electrically  operated  circuit  breakers. 

Ordinarily,  where  current  transformers  are  used  for  instru- 
ments and  watt-hour  meters  the  trip  coils  can  be  connected  to 
the  same  transformers,  if  great  accuracy  is  not  required.  Where 
not  required  for  instruments  or  meters,  lower  priced  transformers 
of  good  accuracy  are  available  for  connection  directly  to  the 
circuit-breaker  trip  coils  or  to  relays. 

Series  Trip. — The  coils  for  series  automatic  overload  trip  are 
either  dry  insulated,  mounted  in  the  switchboard  cover  plate,  or 
they  are  contained  in  the  circuit-breaker  oil  tank.  In  the  former 
case,  the  main  connections  to  the  series  trip  coils  are  made 
through  holes  in  the  panel,  these  holes  being  covered  by  the 
cover  plate.  This  method  of  trip  is  recommended  to  be  applied 
only  to  .small  low  capacity  installations  not  having  current 
transformers  for  meters. 

Tripping  Calibration. — Breakers  automatically  operated  from 
current  transformers  and  current  transformer  trip  coils  or  from 
series  trip  coils  are  usually  calibrated  to  function  through  a 
range  of  from  80  to  160  per  cent,  of  the  normal  current  rating  of 
the  current  transformer  or  of  the  series  trip  coil.  The  tripping 
coils  can  be  set  to  function  at  any  current  within  the  range  given 
on  the  scale.  Since  the  transformer  trip  coils  are  energized  by 
power  from  the  secondaries  of  series  transformers  in  the  main 
circuit,  the  high  voltage  is  removed  from  the  cover  plate  and, 
therefore,  from  the  front  of  the  switchboard  panel  or  other 
operating  station. 

Inverse  Time. — When  inverse  time  limit  is  required  to  prevent 
the  circuit  breaker  coming  out  unnecessarily  on  short  overloads, 
an  adjustable  inverse  time  limit  dashpot  can  be  applied  to  the 
standard  cover  plate  of  some  breakers,  With  various  mixtures 
of  oil,  the  time  limit  can  be  varied  considerably. 


90          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Where  automatic  undervoltage  protection  is  required  or 
where  tripping  is  desired  upon  failure  of  power  rather  than  from 
an  auxiliary  circuit,  an  automatic  undervoltage  trip  can  be 
supplied.  Up  to  600  volts  alternating  current  the  coil  of  this 
attachment  is  shunted  directly  across  the  line  but  on  higher 
voltages  the  coil  is  connected  in  the  secondary  of  a  voltage 
transformer. 

The  automatic  undervoltage-trip  attachment,  as  described 
above,  can  be  supplied  with  a  5-ampere  coil  and  then  used  as  an 
automatic  underload-trip  device  in  connection  with  appropriate 
current  transformers  to  trip  the  circuit  breakers  upon  the  load 
decreasing  below  a  predetermined  amount.  These  are  of  the 
manual  reset  form. 

Automatic  overvoltage-trip  coils  can  be  used  on  circuit 
breakers  to  trip  the  breaker  in  case  the  voltage  of  the  circuit 
increases  to  a  certain  predetermined  setting. 

CONDIT  OIL  CIRCUIT  BREAKERS 

A  very  complete  line  of  oil  circuit  breakers  has  been  put  on  the 
market  by  the  Condit  Electrical  Manufacturing  Company,  of 
South  Boston,  ranging  in  size  from  the  types  G>  I  and  N 
for  industrial  service  and  motor  starting,  the  M  for  manhole 
and  P  for  pole  top  through  the  various  switchboard  types 
E  and  D  to  the  large  capacity  separately  mounted  breakers 
for  compartment  mounting  and  the  outdoor  high  tension 
breakers. 

Motor  Starters. — The  type  G-l  oil  motor  starters  are  used 
for  starting  squirrel-cage  motors  that  do  not  need  any  auto 
starter  or  compensators.  These  are  essentially  double-throw 
breakers  for  currents  up  to  100  amperes  for  motors  up  to  35 
H.P.  In  the  starting  position  the  overload  coils  are  not  in  circuit 
but  as  soon  as  the  motor  gets  up  to  speed  the  breaker  is  thrown 
over  to  the  running  position  when  the  automatic  coils  are  cut  in 
and  time  limit  devices  prevents  a  momentary  current  surge  from 
tripping  out  the  breaker. 

The  type  I  motor  starters  are  somewhat  similar  but  in  place 
of  overload  coils  the  automatic  protection  is  secured  through 
fuses  that  are  cut  out  at  starting  but  in  circuit  during  the  run- 
ning position.  These  are  used  for  motors  up  to  10  H.P.  at  440 
and  550  volts. 

The   N-l    oil   starter   is   suitable   for   circuits   with   starting 


OIL  CIRCUIT  BREAKERS  91 

currents  up  to  150  amperes  at  110  volts,  80  amperes  at  550  volts. 
Its  general  features  correspond  with  the  G-l. 

Entrance  Switches. — The  N-2  oil  circuit  breakers  are  in- 
tended principally  as  entrance  switches  for  a  maximum  current 
of  60  amperes  and  maximum  voltage  of  600.  The  case  is  divided 
into  three  parts:  the  top  contains  the  fuses;  the  middle  carries 
the  switch  mechanism;  the  bottom  forms  the  oil  tank.  While 
this  is  a  non-automatic  device  with  or  without  fuse  clips  it  can  be 
provided  with  shunt-trip  or  undervoltage  release. 

Manhole  Switches. — For  manhole  service  the  M-5  is 
furnished  both  single  throw  and  double  throw  with  cable  sleeves 
for  single  conductor  cable  and  the  M-6  is  furnished  for  single 
throw  only  and  for  multiple  conductor  cables.  The  design  of 
the  operating  mechanism  of  the  M-5  and  M-6  oil  switches  em- 
bodies the  highly  important  feature  of  easy  closure,  and  at  the 
same  time  affords  ample  pressure  at  the  contact  surface.  It  is 
extremely  simple  in  design  and  positive  in  action.  The  bearings 
are  made  of  non-corrosive  metal.  The  handle  not  only  operates 
the  switch,  but,  being  removable,  also  serves  to  insert  and  remove 
the  plug  which  seals  the  switch.  Each  brush  or  bridging  member 
is  built  of  special  hard-drawn  copper  laminae,  so  formed  that  each 
lamina  makes  individual  contact  with  the  stationary  contact 
member  and  allows  a  definite  space  for  the  free  circulation  of 
oil  between  adjacent  laminae.  The  brushes  make  contact  with 
a  long-wiping,  self -cleaning  action.  They  are  secured  to  specially 
treated  wood  rods  in  such  a  manner  that  they  are  self-aligning, 
insuring  each  individual  lamina  carrying  its  full  share  of  the  cur- 
rent. This  construction  gives  the  laminated  brush  decidedly 
excellent  current-carrying  features.  Each  brush  is  protected  by 
two  auxiliary  arcing  tips  made  of  relatively  heavy,  special 
shaped,  hard-drawn  copper.  They  are  mounted  on  the  extremi- 
ties of  a  spring  support  fastened  to  the  lower  portion  of  the  brush 
so  as  to  make  contact  with  similar  stationary  arcing  tips  fas- 
tened to  the  stationary  contact  member.  Each  of  these  arcing 
tips  is  easily  renewable  and  reversible,  giving  approximately 
twice  the  usual  length  of  service,  and  decreases  the  maintenance 
cost  of  the  switch  correspondingly. 

Pole  Switches. — Pole  line  oil  switches,  type  PK-5,  are  for 
weatherproof  service  and  are  used  for  the  sectionalizing  of  lines, 
switching  of  transformer  banks  and  similar  service.  They  are 
suitable  for  use  on  alternating-current  circuits  where  the 


92          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

current  does  not  exceed  200  amperes  at  pressure  of  4500  volts 
or  less. 

The  mechanism  is  extremely  simple  in  construction  and  is 
enclosed  in  a  substantial  weatherproof  iron  case.  The  cover  is 
provided  with  an  overhanging  rim,  securely  fastened  by  swinging 
bolts  and  wing  nuts,  permitting  easy  access  to  the  interior.  A 
depending  projection  on  the  front  of  the  cover  serves  as  an  effi- 
cient watershed  for  the  operating  handle  and  prevents  the  forma- 
tion of  ice  and  sleet  from  interfering  with  the  operation  of  the 
switch. 

The  oil  tank  is  made  of  heavy  sheet  metal  with  welded  joints, 
combining  strength  and  rigidity,  and  is  fastened  to  the  frame  by 
means  of  swinging  bolt  and  wing-nut  construction,  thus  allowing 
the  tank  to  be  readily  removed  without  disturbing  any  of  the 
operating  parts. 

The  tank  is  provided  with  a  suitable  lining,  and  barriers  are 
interposed  between  the  poles  to  give  additional  protection  against 
arcing  under  severe  conditions. 

Single-tank  Breakers. — The  E  line  of  breakers  is  distin- 
guished by  having  all  poles  of  the  breaker  in  the  same  tank. 
The  E-3  breakers  are  arranged  for  panel  mounting,  panel  frame 
mounting  or  remote  control  by  hand  or  solenoid.  Series  trip 
coils  or  current  transformer  trip  can  be  used  and  a  rupturing 
capacity  of  1600  amperes  at  4500  volts,  3300  at  2500  can  be 
guaranteed. 

Type  E-3. — Condit  type  E-3  oil  circuit  breakers,  Fig.  55,  have 
been  designed  primarily  for  controlling  and  protecting  feeder 
circuits,  transformer  banks,  generators,  etc.,  where  moderate 
interrupting  capacity  is  required.  They  are  made  in  two, 
three  and  four  poles,  single  and  double  throw,  automatic  and 
non-automatic,  for  manual  and  electrical  operation.  All  of  the 
automatic  forms  may  be  provided  with  undervoltage,  shunt- 
trip  and  time  limit  attachments.  Auxiliary  switches  of  the 
circuit  opening  and  circuit  closing  type  may  also  be  utilized  in 
connection  with  either  the  non-automatic  or  automatic  form. 

The  automatic  form  may  be  furnished  in  either  series,current 
transformer,  or  relay  trip.  Type  E-3  series  trip  oil  breakers  have 
a  maximum  capacity  of  200  amperes,  and  may  be  used  where  the 
pressure  does  not  exceed  2500  volts. 

Non-automatic  and  current  transformer  or  relay  trip  oil  circuit 
breakers  are  furnished  in  capacities  up  to  and  including  300 


OIL  CIRCUIT  BREAKERS 


93 


amperes,  and  may  be  used  where  the  pressure  does  not  exceed 
4500  volts.  They  are  furnished  for  panel,  panel  frame  or  pipe 
frame  mounting  for  direct  control,  and  are  arranged  for  flat 
surface  or  pipe  frame  mounting  for  manual  remote  control  or 
electrical  remote  control.  Double-throw  switches  and  circuit 
breakers  are  arranged  for  panel  mounting  only. 


FIG.  55. — Condit  Electric  &  Mfg.  Co.  oil  circuit  breaker,  type  E3,  single  throw. 


All  automatic  type  E-3  overload  circuit  breakers  have  their 
trip  coils  and  calibration  adjustments  on  the  front  of  the  switch- 
board, and  the  mechanism  is  arranged  to  prevent  the  operator 
from  holding  the  switch  closed  during  an  overload  or  short 
circuit.  The  mechanism  is  capable  of  adjustment  to  suit  the 
conditions  of  installation. 

Studs. — The  studs  are  copper  rod  of  sufficient  cross-section 
to  properly  carry  their  rated  current  continuously,  and  are 
insulated  from  the  frame  by  high-grade,  well-glazed  porcelain 
bushings,  thus  affording  ample  insulation.  The  top  of  the  stud 


SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


is  threaded  to  receive  the  terminal  to  which  line  conductors  may 
be  connected.  Fastened  to  the  lower  end  is  a  stationary  contact 
member  on  which  is  mounted  the  stationary  arcing  tips. 

The  terminals  are  enclosed  in  an  insulating  sleeve  in  order  to 
prevent  accidental  contact  with  the  live  parts. 

Tank. — The  oil  tank  is  made  of  heavy  sheet  metal  with  welded 
joints,  combining  strength  and  rigidity.  The  tank  fits  inside  of 
an  overhanging  rib  which  forms  a  part  of  the  cover  or  frame  of  the 
breaker.  This  rib  construction  materially  reinforces  the  tank 
and  prevents  its  sides  from  bulging  outwards,  even  when  sub- 
jected to  excessive  pressure  from  within.  It  is  fastened  to  the 
cover  or  frame  by  means  of  heavy  tank  bolts  and  wing  nuts, 

thus  allowing  the  tank  to  be 
readily  removed  for  inspec- 
tion, without  disturbing  any 
of  the  operating  parts.  The 
tank  is  provided  with  a  suit- 
able lining  and  barriers  are 
supplied  between  the  poles  to 
give  additional  protection 
against  arcing  under  severe 
conditions.  An  oil  line  on 
the  outside  of  the  tank  indi- 
cates the  height  to  which  the 
tank  should  be  filled  with  oil 
when  removed  from  the 
breaker. 

Type  E-4.— Fig.  56  shows 
the  arrangement  of  the  panel 
mounting,  double-throw 
breaker,  with  the  two  inter- 
locked closing  handles.  These 
type  E-4  breakers  are  made  in  capacities  of  300  and  500  amperes 
at  7500  volts  and  800  at  4500  for  rupturing  capacities  of  1700 
amperes  at  7500  volts  for  the  300  and  500  ampere  sizes,  3160  at 
4500  for  all  sizes,  6100  at  2500  for  all  sizes,  and  15,000  for  the 
300  and  500  at  750,  and  20,000  at  750  for  the  300  ampere  size. 
Their  general  features  correspond  closely  with  those  described 
for  the  E-3. 

All  automatic  type  E-4  overload  circuit  breakers  have  their 
trip  coils  and  calibration  adjustments  on  the  front  of  the  switch- 


FIG.  56. — Condit  Electric  &  Mfg.  Co. 
oil  circuit  breaker,  type  E4,  double 
throw. 


OIL  CIRCUIT  BREAKERS 


95 


board,  and  the  mechanism  is  arranged  to  prevent  the  operator 
from  holding  the  switch  closed  during  an  overload  or  short 
circuit. 

Fig.  57  shows  the  arrangement  of  the  800-ampere  4500-volt 
type  E-4  breaker  hand  operated,  remote  control. 


Fia.  57. — Condit  Electric  &  Mfg.  Co.  oil  circuit  breaker,  type  E4,  hand  operated, 
remote  control. 

Motor  Starters. — The  type  E-6  oil  starter  is  a  combination  of  a 
switch  and  a  circuit  breaker,  used  for  controlling  and  protecting 
induction  and  self -starting  synchronous  motors  whose  continuous 
full-load  current,  including  overloads,  does  not  exceed  200  am 
peres  at  pressures  of  2500  volts  or  less. 

They  are  used  extensively  for  starting  squirrel-cage  induction 
motors  without  the  use  of  auto  transformers  or  compensators. 


96          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Three-pole  switching  equipment  is  furnished  for  use  with  3-phase 
or  3-wire,  2-phase  induction  motors,  and  4-pole  switching  equip- 
ment is  furnished  for  use  with  2-phase  motors  supplied  from 
4-wire,  2-phase,  non-interconnected  systems.  Type  E-6  oil 
starters  are  made  3  or  4-pole,  manually  operated,  panel  mount- 
ing only,  arranged  for  series  or  current  transformer  trip  with 
time  limit  attachments  and  selective  mechanical  interlock. 
They  may  also  be  provided  with  under- voltage  and  shunt-trip 
attachments. 

The  faceplate  is  provided  with  two  handles.  The  handle  on 
the  left  operates  the  starting  switch  and  cannot  be  latched  closed. 
The  handle  on  the  right  operates  the  circuit  breaker  which  pro- 
tects the  motor,  when  running,  from  short  circuit,  overload,  and 
single  phase  running. 

The  trip  coils  and  calibration  adjustments  are  conveniently 
located  on  the  front  of  the  panel. 

Type  E-7. — The  type  E-7  oil  starter  is  a  combination  of  a 
switch  and  a  circuit  breaker,  used  for  controlling  3-phase 
induction  or  self-starting  synchronous  motors  whose  continuous 
full-load  current,  including  overloads,  does  not  exceed  200  am- 
peres at  pressures  of  2500  volts  or  less.  These  oil  starters  are 
arranged  only  for  3-wire,  3-phase,  and  3-wire,  2  phase,  alternating 
current  motors.  They  are  not  suitable  for  use  on  4-wire,  2  phase, 
non-interconnected  systems.  They  may  be  used  in  connection 
with  auto  transformers  having  either  2  or  3  exciting  coils,  and 
are  made  4-pole,  manually  operated,  panel  mounting  only, 
arranged  for  series  or  current  transformer  trip  with  time  limit 
attachments  and  selective  mechanical  interlock.  They  may  also 
be  provided  with  undervoltage  and  shunt-trip  attachments. 

The  faceplate  is  provided  with  two  handles.  The  handle  on 
the  left  operates  the  starting  switch  and  cannot  be  latched 
closed.  The  handle  on  the  right  operates  the  circuit  breaker 
which  affords  protection  against  short  circuit,  overload  and  single- 
phase  running. 

Independent  Tank  Breakers. — Type  D-12  circuit  breakers 
have  independent  tanks  for  each  pole  of  the  breaker  but  all 
poles  on  the  same  frame.  These  breakers  have  a  guaranteed 
rupturing  capacity  of  1250  amperes  at  15,000  volts;  2500  at 
7500;  4200  at  4500,  and  7500  at  2500  volts.  The  300,  500  and 
800  amperes  at  2500  volts  are  made  for  panel  frame  mounting 
and  all  of  the  other  ratings  for  distant  control  only.  They  are 


OIL  CIRCUIT  BREAKERS 


97 


used  to  meet  the  demands  in  controlling  and  protecting  electrical 
circuits  and  apparatus  where  the  pressure  does  not  exceed  15,000 
volts.  They  are  well  adapted  for  installations  where  space 
requirements  are  an  important  factor,  and  a  relatively  high 
interrupting  capacity  is  desired.  They  are  used  principally  to 
control  feeder  circuits  in  substations  of  large  distribution  systems 


FIG.  58. — Condit  Electric  &   Mfg.  Co.  oil  circuit  breaker,  type  D12,  frame 
mounted. 

and  for  the  control  and  protection  of  generators  and  feeders  in 
industrial  service  where  a  relatively  high  rupturing  capacity  is 
required  at  moderate  voltages. 

All  automatic  type  D-12  overload  circuit  breakers  have  their 
trip  coils  and  calibration  adjustments  on  the  front  of  the  switch- 
board, and  the  mechanism  is  arranged  to  prevent  the  operator 
from  holding  the  switch  closed  during  an  overload  or  short 
circuit.  They  are  furnished  for  current  transformer  trip  or  non- 


98          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

automatic,  as  panel  frame  mounting  shown  in  Fig.  58,  2500  volts 
or  less  where  the  current  does  not  exceed  800  amperes.  For 
flat  surface  (wall  or  cell  mounting)  or  for  pipe  frame  mounting, 
they  can  be  supplied  manually  operated  remote  control  and  elec- 
trically operated  for  4500  volts  or  less  where  the  current  does  not 
exceed  1200  amperes;  7500  volts  or  less  where  the  current  does 
not  exceed  1000  amperes;  15,000  volts  or  less  where  the  current 
does  not  exceed  800  amperes. 

Electrically  operated. — This  type  of  D-12  oil  circuit  breakers, 
Fig.  59  is  furnished  in  the  standard  ampere  capacities,  poles, 
and  mountings  at  the  various  voltages.  They  consist  of  the 


FIG.  59. — Condit  Electric  &  Mfg.  Co.  oil  circuit  breaker,  type  D12,  solenoid 
operated,  1200  amps. 

standard  manually  operated  breaker  equipped  with  a  closing 
magnet,  opening  magnet,  control  relay,  control  switch  with  red 
and  green  indicating  lamps,  and  one  indicating  lamp  switch. 

Terminals  up  to  and  including  800  amperes  are  enclosed  in  an 
insulating  sleeve  to  prevent  accidental  contact  with  live  parts. 
Circuit  breakers  in  excess  of  800  amperes  are  provided  with 
laminated  terminals  to  which  cable  terminals  or  flat  copper 
connections  may  be  bolted. 

Each  pole  of  the  D-12  oil  circuit  breakers  is  provided  with  an 
individual  oil  tank  made  of  3^-inch  steel  with  welded  seams,  and 
is  provided  with  a  suitable  lining.  Each  tank  is  fastened  to  the 
frame  by  a  strong  tank  bolt  construction,  which  allows  ready 


OIL  CIRCUIT  BREAKERS 


99 


removal  for  inspection  without  disturbing  any  of  the  operating 
parts. 

A  depending  flange,  which  serves  to  strengthen  the  frame, 
prevents  any  tendency  to  tank  distortion  when  circuit  breakers 
are  called  upon  to  interrupt  the  circuit  under  severe  conditions. 
An  oil  line  on  the  outside  of  each  tank  indicates  the  height  to 
which  the  tank  should  be  filled  with  oil  when  removed  from  the 
breaker. 


FIG.    60. — Condit    Electric  &  Mfg.   Co.   oil  circuit  breaker,   type  D13,   hand 
operated,  remote  control. 

Type  D-13. — The  D-13  oil  circuit  breakers  have  a  guaranteed 
rupturing  capacity  of  1000  amperes  at  25,000  volts  for  the  300 
and  500  ampere  sizes;  1700  at  15,000,  3500  at  7500,  5800  at 
4500,  and  10,000  at  2500  for  all  sizes.  They  are  made  in  single, 
2-,  3-,  and  4-poles,  for  manual  remote  control  or  electrical 
operation  with  separate  tanks  per  pole.  They  are  furnished 


100        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

in  300,  500  and  800-ampere  capacity  for  pressures  of  15,000  volts 
or  less,  and  for  capacities  of  300  and  500  amperes  where  the 
pressure  does  not  exceed  25,000  volts.  This  type  is  adapted  for 
flat  surface  mounting  on  either  walls  or  in  cells,  or  it  may  be 
mounted  on  pipe  frame  structures. 

Mechanism. — Each  pole  of  the  D-13  oil  circuit  breakers, 
Fig.  60,  is  provided  with  an  operating  mechanism  of  unique 
design.  The  upper  extremity  of  the  brush  rod  is  provided  with 
a  threaded  ferrule  fastened  so  as  to  give  maximum  mechanical 
strength.  The  ferrule  and  rod  are  threaded  into  a  pivoted 
cross-head  at  the  end  of  the  operating  mechanism  which  travels 
with  a  straight-line  motion.  This  construction  serves  as  a 
brush  adjustment  and  maintains  the  brush  rigidly  in  its  proper 
position  in  relation  to  the  stationary  contact  members.  The 
brush  is  fastened  in  a  self-aligning  manner  to  the  lower  extremity 
of  the  brush  rod. 

The  mechanism  closes  easily  and  at  the  same  time  affords 
ample  pressure  at  the  contact  surface.  It  is  designed  particu- 
larly to  allow  rapid  acceleration  of  the  movable  contact 
members  during  the  initial  opening  of  the  circuit.  Each  of  the 
individual  poles  is  operated  through  a  common  shaft,  which 
may  be  actuated  either  manually  or  electrically. 

Attachments. — Undervoltage  attachments  for  D-12  and  D-13 
breakers  are  designed  so  that  the  breakers  will  be  released  when 
the  pressure  drops  to  approximately  50  per  cent,  of  its  normal 
value.  Shunt-trip  attachments  are  provided  with  a  heavy 
tripping  spring,  which  insures  positive  action.  They  are  wound 
for  voltages  of  110,  220,  440,  and  550,  for  either  direct  or  alter- 
nating current,  25  or  60  cycles,  and  have  an  operating  range  from 
55  to  115  per  cent,  normal  voltage. 

Many  forms  of  devices,  such  as  relays  and  time  limit  attach- 
ments, may  be  used  in  conjunction  with  type  D-12  oil  circuit 
breakers  for  the  purpose  of  causing  their  operation  in  accordance 
with  predetermined  conditions.  Type  D-12  oil  circuit  breakers 
may  be  furnished  with  time  limit  attachments  applied  directly  to 
the  calibration  tubes,  in  capacities  up  to  and  including  800  am- 
peres. Time  limit  attachments  are  not  furnished  for  1000  am- 
peres and  above. 

Heavy-current  Types. — Type  Y-l  and  Y-2  oil  circuit  breakers 
are  used  on  circuits  of  moderate  voltage  and  relatively  large 
ampere  capacity,  for  the  control  and  protection  of  generators, 


OIL  CIRCUIT  BREAKERS  101 


FIG.  61.— Condit  Electric  &  Mfg.  Co.  oil  circuit  breaker,  type  Yl. 


FIG.  62. — Condit  Electric  &  Mfg.  Co.  oil  circuit  breaker,  type  Y2. 


102        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

motors,  transformer  banks,  feeder-circuits,  as  service  entrance 
switches,  etc. 

Type  Y-l. — These  oil  circuit  breakers  as  shown  in  Fig.  61  are 
made  3  and  4-pole,  automatic  and  non-automatic,  for  manual 
remote- control  and  electrical  remote-control  operation.  All  of 
the  automatic  forms  may  be  provided  with  undervoltage  and 
shunt  trip.  They  are  furnished  for  use  on  circuits  where  the 
pressure  does  not  exceed  2500  volts  and  the  current  does  not 
exceed  2500  amperes  at  60  cycles,  or  3000  amperes  at  25  cycles. 

Type  Y-2. — These  oil  circuit  breakers,  Fig.  62,  are  made  3-pole 
only,  for  use  on  circuits  where  the  pressure  does  not  exceed  2500 
volts,  and  where  the  maximum  capacity  does  not  exceed  4500 
amperes  at  60  cycles,  or  5500  amperes  at  25  cycles.  Auxiliary 
switches  of  the  circuit  opening  and  circuit  closing  type  may  be 
utilized  in  connection  with  either  the  automatic  or  non-automatic 
forms. 

Ratings. — The  Y-l  breakers  are  made  in  25-cycle  ratings  of 
1800,  2400  and  3000,  amperes  with  corresponding  60-cycle  ra- 
tings of  1500,  2000,  and  2500.  The  Y-2  breaker  has  a  60-cycle 
rating  of  4500  amperes  and  a  25-cycle  rating  of  5500.  The 
guaranteed  rupturing  capacities  of  the  Y-l  are  7500  amperes  at 
2500  volts,  30,000  at  750,  while  for  the  Y-2  the  rupturing  capaci- 
ties are  15,000  at  2500  volts,  50,000  at  750. 

Each  pole  of  the  type  Y  oil  circuit  breakers  is  provided  with  an 
individual  steel  oil  tank  with  welded  seams.  Each  tank  is 
fastened  to  the  frame  by  a  strong  tank  bolt  construction  which 
allows  ready  removal  for  inspection  without  disturbing  any  of 
the  operating  parts. 

A  rugged,  box-shaped  frame  carries  the  operating  mechanism, 
to  which  is  securely  fastened  a  heavily  ribbed,  non-magnetic 
metal  cover  which  serves  as  a  support  for  the  insulating  bush- 
ings, studs  and  oil  tanks. 

Brushes. — Each  brush  or  bridging  member,  shown  in  Fig.  63  is 
built  up  of  special  hard-drawn  copper  laminae,  so  formed  that  each 
lamina  makes  individual  contact  with  the  stationary  contact 
member  and  allows  a  definite  space  for  the  free  circulation  of  oil 
between  adjacent  laminse.  The  brushes  make  contact  with  a 
long-wiping,  self -cleaning  action.  Each  brush  is  suspended  by  an 
individual,  specially  treated  wood  rod,  in  such  a  manner  that  the 
brushes  are  self-aligning  in  relation  to  the  stationary  contact 
members.  This  construction  permits  of  easy  and  convenient 


OIL  CIRCUIT  BREAKERS  103 

individual  brush  adjustment,  without  the  use  of  shims — a  feature 
of  great  importance  in  apparatus  for  this  class  of  equipment. 

The  studs  are  insulated  from  the  supporting  frame  by  moulded 
insulation  designed  particularly  to  withstand  mechanical  strains 
incident  to  the  operation  and  installation  of  oil  circuit  breakers 
of  large  ampere  capacity.  The  studs  are  made  up  of  laminated 
copper  bars,  each  4-inch  by  ^-inch,  the  number  depending  upon 
the  ampere  capacity.  The  top  of  the  stud  is  arranged  to  receive 
3^-inch  bar  connections  or  cable  terminals  to  receive  the  line 
conductors.  Fastened  to  the  lower  end  of  the  stud  is  the  sta- 
tionary contact  member  on  which  are  mounted  the  stationary 
arcing  tips. 


FIG.  63. — Condit  Electric  &  Mfg.  Co.  brush  construction  type  "Y2"  oil  current 
breaker. 

Each  brush  unit  is  protected  by  two  extra  heavy,  special- 
shaped  auxiliary  arcing  tips  made  of  hard-drawn  copper.  They 
are  mounted  on  the  extremities  of  a  spring  support  fastened  to  the 
lower  portion  of  the  brush,  so  as  to  make  contact  with  similar 
stationary  arcing  tips.  Each  of  these  arcing  tips  is  easily  re- 
newable and  reversible,  giving  approximately  twice  the  usual 
length  of  service  and  decreasing  the  maintenance  cost  corre- 
spondingly. 

Cell  Mounting. — The  type  F-6  oil  circuit  breakers,  Fig.  64, 
are  furnished  3-pole  only,  cell  mounting,  in  500  and  800  ampere 
capacities  where  the  pressure  does  not  exceed  15,000  volts.  They 
may  be  arranged  for  either  hand  remote  control  or  electrical 
operation  and  embody  distinctive  features  which  make  them 
highly  desirable  for  installations  where  continuity  of  service  is 
essential. 

Construction. — The  renewable  unit  construction  is  employed 
in  connection  with  the  type  F-6  oil  circuit  breaker,  as  this  renders 
the  quickest  possible  means  of  replacement,  repair  or  inspection. 
The  operating  mechanism  is  entirely  enclosed  in  the  expansion 


104        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

chamber,  which  is  firmly  fastened  to  a  34-inch  steel  tank 
supported  on  a  three-point  truck  to  facilitate  easy  handling. 
The  electrically  operated  mechanism  is  compact,  of  simple 
design,  and  is  mounted  above  the  switch  units.  The  conductors 
may  be  brought  to  the  circuit  breaker  either  through  the  top  or 
rear  of  the  cell. 


FIG.  64. — Condit  Electric  &  Mfg.  Co.  oil  circuit  breaker,  type  F6. 

The  important  features  of  design  which  characterize  the  type  F-6 
oil  circuit  breakers  are  the  efficient  laminated  brush,  reversible 
and  easily  renewable  arcing  tips,  self-aligning,  sure  seating 
action  between  the  movable  contact  members  and  the  station- 
ary contact  members,  the  rugged  tank-per-pole  construction, 


OIL  CIRCUIT  BREAKERS 


105 


FIG.  65. — Condit  Electric  &  Mfg.  Co.  oil  circuit  breaker,  type  D15  floor 
mounting. 


FIG.  66. — Condit  Electric  &  Mfg.  Co.  oil  circuit  breaker,  type  D15,  frame 
mounting. 


106        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

high  head  of  oil  over  break,  large  expansion  chamber  and  the 
strong  spring  action  inherent  in  the  brushes  which  facilitates 
rapid  acceleration  of  the  movable  contact  members  on  the  initial 
opening  of  the  circuit. 

High  Voltage  Breakers. — Type  D-15  oil  circuit  breakers  are 
furnished  for  indoor  application  for  the  control  and  protection 
of  transmission  lines,  transformer  banks,  etc.,  where  the  normal 
operating  voltage  is  44,000  volts  or  less.  The  type  R-l  oil  cir- 
cuit breakers  are  used  where  the  normal  operating  voltage  is 
70,000  volts  or  less.  For  outdoor  application,  type  D-16  oil 
circuit  breakers  are  furnished. 

Type  D-15. — These  -oil  circuit  breakers  are  made  3-pole 
only,  arranged  for  manual  direct  control,  manual  remote  control 
or  electrical  remote  control.  They  are  furnished  in  the  following 
standard  ampere  capacities:  300  amperes,  44,000  volts  or  less; 
300,  500  and  800  amperes,  25,000  volts  or  less.  They  are  made 
in  two  forms  of  mounting:  floor  mounting,  where  the  tanks  rest 
on  the  floor,  as  shown  on  Fig.  65  and  frame  mounting,  as  shown 
on  Fig.  66. 

They  consist  essentially  of  three  separate,  identical  units, 
sufficiently  spaced  so  that  cell  walls  and  barriers  are  usually  un- 
necessary. Each  unit  consists  of  a  strong,  well  ribbed  cover, 
forming  a  large  expansion  dome.  This  cover  supports  the  me- 
chanism and  conducting  parts.  The  oil  tank  is  securely  fastened 
to  the  expansion  dome,  and  is  provided  with  an  oil  gauge  and 
oil  drain. 

The  D-15  oil  circuit  breakers  are  characterized  by  the  laminated 
brush,  reversible  and  easily  renewable  arcing  tips,  the  rugged 
tank  construction,  large  expansion  chamber,  and  the  strong  spring 
action  of  the  brushes  which  facilitates  rapid  acceleration  of  the 
moving  contact  members  upon  the  initial  opening  of  the  circuit. 
They  are  furnished  for  current  transformer  and  relay  trip. 

Type  D-16. — These  oil  circuit  breakers  are  furnished  for 
outdoor  application  for  the  control  and  protection  of  transmission 
lines,  transformer  banks,  etc.,  where  the  normal  operating  volt- 
age is  44,000  volts  or  less.  They  are  made  3-pole  only, 
arranged  for  manual  direct  control  or  electrical  remote  control 
and  are  furnished  in  the  following  ampere  capacities :  300  amperes 
44,000  volts  or  less;  300,  500  and  800  amperes,  25,000  volts  or  less. 

The  D-16  oil  circuit  breakers  are  made  in  two  forms  of  mount- 
ing :  floor  mounting,  where  the  tanks  rest  on  the  floor,  and  frame 


OIL  CIRCUIT  BREAKERS 


107 


mounting,  Fig.  67,  where  the  tanks  are  supported  by  a  frame 
structure.  They  consist  essentially  of  three  separate,  identical 
units,  so  arranged  with  relation  to  a  common  operating  mechan- 
ism as  to  cause  simultaneous  operation  of  the  contact  members. 
Each  unit  consists  of  a  strong,  well  ribbed  cover,  forming  a  large 
expansion  dome.  This  cover  supports  the  mechanism,  bushings 
and  weatherproof  hood.  The  oil  tank  is  securely  fastened  to 


FIG.  67. — Condit  Electric  &  Mfg.  Co.  oil  circuit  breaker,  type  D16,  frame 
mounting. 


the  expansion  dome  and  is  provided  with  an  oil  gauge  and  oil 
drain.  These  oil  circuit  breakers  are  characterized  by  large 
expansion  chamber  with  baffled  gas  vents,  substantial  tank 
construction,  reversible  and  easily  renewable  arcing  tips,  and 
efficient  laminated  brush,  the  strong  spring  action  of  which 
facilitates  rapid  acceleration  of  the  moving  contact  members  upon 
the  initial  opening  of  the  circuit. 


108        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

GENERAL  ELECTRIC  OIL  BREAKERS 

The  General  Electric  Company  early  advocated  the  use 
of  the  oil  circuit  breaker  for  A.C.  service  and  have  done  a  great 
deal  of  pioneer  work  in  developing  breakers  suitable  for  various 
classes  of  service.  Their  earlier  designs  have  naturally  been 
superseded  by  later  modifications  embodying  the  improvements 
that  experience  has  shown  to  be  advantageous. 

Lines. — There  are  a  number  of  different  lines  of  breakers  to 
take  care  of  the  different  classes  of  work.  For  the  small  in- 
dustrial service,  there  are  the  TP-10'  and  similar  breakers; 
for  the  moderate  capacity  moderate  voltage  breakers  for  switch- 
board service  the  'K-5'  and  'K-12'  breakers  are  being  super- 
seded by  the  'K-32'  and  'K-35,'  while  for  moderate  voltages 
and  high  rupturing  capacity  the  'H-3,'  'H-6,'  and  'H-9' 
breakers  are  utilized  and  the  high  voltage  circuits  are  taken  care 
of  by  the  'K-24,'  'K-26,'  <K-36/  etc. 

Industrial. — For  industrial  service  the  TP-10'  breaker  is 
built  in  capacities  up  to  50  amperes  for  600  volts,  is  arranged 
for  conduit  wiring  and  is  suitable  for  induction  motors  up  to 
25  H.P. 

The  automatic  breaker  is  provided  with  two  series  inverse 
time  overload  trip  coils,  mounted  inside  the  cover.  Dashpots  and 
calibrating  tubes  are  covered  by  a  drawn  steel  casing  attached 
to  breaker  frame.  The  breaker  cannot  be  held  closed  on  overload 
or  short  circuit.  The  undervoltage  breaker  can  be  furnished 
triple  or  four-pole  with  a  self-setting  undervoltage  release  attach- 
ment mounted  inside  the  breaker  frame  which  trips  the  breaker 
if  the  voltage  of  the  line  drops  to  approximately  50  per  cent,  of 
normal. 

The  non-automatic  breaker  is  similar  to  undervoltage  and 
overload  forms  except  there  is  no  tripping  attachment  and  operat- 
ing mechanism  is  slightly  different. 

The  combined  overload  and  undervoltage  breaker  is  made 
triple-pole  with  undervoltage  release  and  overload  protective 
plugs;  four-pole  with  undervoltage  release  and  double-series 
overload  trip.  Both  protective  plugs  and  series  coils  with  time 
delay  provide  protection  to  motor  when  starting.  Four-pole 
breaker  is  used  triple-pole  by  omitting  connections  to  one  set  of 
contacts. 

The  cover  is  a  single  piece  of  sheet  steel  and  fits  tightly  over  the 
top  of  the  breaker  frame  which  is  a  light  but  strong  sheet-steel 


OIL  CIRCUIT  BREAKERS  109 

box  which  supports  all  parts  of  the  breaker.  The  words  "off" 
and  "on"  on  the  frame  indicate  whether  the  breaker  is  open  or 
closed.  Oil  dashpots  give  time  delay  to  automatic  overload 
trip  which  can  be  set  to  remain  inactive  on  starting  current  of 
motor  but  to  trip  out  breaker  on  sustained  overloads,  including 
those  caused  by  single-phase  operation. 

The  operating  handle  is  the  only  movable  part  of  breaker 
not  enclosed.  On  opening  this  form  of  breaker  manually,  the 
handle  is  moved  some  distance  to  the  left  before  the  contacts 
begin  to  part,  after  which  they  are  snapped  quickly  open  by  a 
torsion  spring  on  the  operating  shaft. 

The  fixed  contacts  are  copper  fingers  flared  at  lower  end  to 
form  arcing  tips.  Contact  studs  are  securely  held  in  a  porcelain 
block. 

The  movable  contacts  are  mounted  in  a  porcelain  block,  and 
consist  of  copper  strips  bent  to  form.  The  arc,  on  opening 
breaker  under  load,  is  confined  to  the  stationary  arcing  tips  and 
upper  ends  of  movable  contacts,  and  does  not  affect  the  working 
contact  surfaces.  Contacts  are  always  kept  clean  and  will  last 
a  long  time  even  under  rough  usage. 

All  combinations,  both  automatic  and  non-automatic,  except 
the  triple-pole,  plain  undervoltage  breaker  and  the  combined 
undervoltage,  protective  plug  breaker  can  be  furnished  either 
with  the  quick  break,  or  quick  make  and  quick  break  mechanism. 
Quick  break  is  a  feature  of  all  these  breakers.  Breakers  with 
both  quick  make  and  quick  break  mechanism  are  especially 
adapted  for  shipper  rod  operation. 

Textile. — A  modification  of  this  breaker  known  as  the  'FP- 
15'  is  made  for  non-automatic  service,  particularly  for  motors  on 
textile  machinery,  and  the  operation  is  either  manually  or  by 
shipper  rod.  They  can  be  used  to  great  advantage  to  replace 
knife  switches  as  their  safety  features  make  the  breaker  dust- 
proof  and  fireproof  as  well  as  guarding  the  operator. 

Pole  Line. — For  pole  line  service  the  TP-7'  is  intended  for 
mounting  on  any  vertical  flat  surface  and  is  supported  on  the  side 
opposite  the  operating  handle.  The  frame  is  a  cast-iron  box 
which  supports  all  parts  of  switch  and  is  provided  with  a  cast- 
iron  cover  fastened  to  frame  by  four  eye  bolts  with  wing  nuts. 
Porcelain  entrance  bushings  are  used  for  all  cables  entering  the 
switch.  The  fixed  contacts  are  drop-forged  copper  fingers 
flared  at  lower  end  to  form  arcing  tips  while  the  movable  contact 


110        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


blades  are  wedge-shaped,  which  confines  arc  to  top  edge  of  blade 
and  flared  portion  of  contact  fingers.  The  oil  vessel  is  made  of 
heavy  sheet  metal  lined  with  laminated  wood  and  barriers  of 
same  material  between  poles. 

Old  K-5  and  K-12. — Some  of  the  older  designs  of  type  'FE- 
S' and  'FK-12'  were  built  with  insulators  suitable  for  15,000 
volt  service  for  the  500-ampere  size,  this  being  modified  by  using 
shorter  porcelains  with  extension  pieces  under  the  oil  to  utilize 
the  same  moving  parts  and  to  secure  the  same  depth  of  oil  over 
the  contacts  for  2500-volt  service,  and  for  600-volt  service.  The 
rupturing  capacities  assigned  to  the 
FK-5  for  their  various  voltages  were 
1700  at  7500,  2600  at  4500,  5300 
at  2500  and  15,000  at  600  volts. 

The  contacts  for  these  breakers 
are  usually  made  with  flared  copper 
fingers  supported  by  heavy  steel 
springs.  The  movable  contacts  had 
wedge-shaped  copper  blades  slotted 
at  the  apex  in  such  a  way  that  oil  is 
forced  through  the  slots  into  the  arc. 
Modifications  of  this  breaker  with 
independent  poles  placed  in  masonry 
compartments  were  used  for  large 
capacities  and  high  voltages. 

Modern  Types. — The  more  mod- 
ern types  of  FK-12  breakers  are 
built  in  capacities  of  300,  500,  and 
800  amperes  with  a  single  blade 
contact,  while  the  FK-12B  is  made 
with  a  single  blade  for  1000  amperes 
1200  and  1500  amperes,  the  latter 


FIG.  68. — General  Electric  Co.  oil 
circuit  breaker  type  "FK12." 


and  with  double  blades  for 
arrangement  being  shown  in  Fig.  68. 

The  frame  is  a  single  metal  casting,  supporting  all  of  the 
breaker  parts.  Suspended  from  it  is  the  oil  tank  of  heavy  sheet 
metal  with  welded  joints.  The  oil  tanks  of  single-pole  breakers 
are  lined  with  fibre  and  those  of  the  multipole  breakers  with 
treated  laminated  wood.  Multipole  breakers  have  barriers  of 
the  same  special  wood  between  poles. 

The  operating  mechanism,  carried  on  the  frame,  is  designed  to 
produce  parallel  movement  of  the  blades  with  the  breaker  opening 


OIL  CIRCUIT  BREAKERS  111 

by  gravity  assisted  by  the  springs  on  the  contact  fingers  and  on 
the  mechanism.  The  operating  rods  attached  to  the  mechanism 
are  made  of  specially  treated  wood,  screwed  and  clamped  into 
the  crosshead  and  into  the  movable  contact  blade.  This  blade 
is  wedge-shaped,  confining  the  arc  to  the  top  of  the  blade  and 
protecting  the  actual  contact  surface  from  the  damaging  effect 
of  the  arc. 

The  fixed  contacts  are  drop-forged  copper  fingers  secured  to 
the  blocks  at  the  lower  end  of  the  terminal  studs.  The  fingers 
are  flared  at  the  tips  and  one  set  is  extended  to  act  as  arcing  tips. 
These  contact  studs  and  clip  blocks  are  of  one-piece  solid  drop- 
forged  copper,  placed  in  bushings  of  one-piece  glazed  porcelain 
extending  below  the  level  of  the  oil.  The  bushing  clamps  are 
interchangeable  metal  plates  with  trued  surfaces  which  firmly 
secure  the  insulator  to  the  frame  in  proper  alignment. 

Ratings. — The  rupturing  capacities  assigned  to  the  FK-12 
and  FK-12-B  breakers  built  for  various  voltages  are  700  amperes, 
at  22,000  volts,  1200  at  15,000,  2760  at  7500,  4840  at  4500, 
9000  at  2500  and  30,000  amperes  at  750  volts. 

Type  K-32.— These  FK-12  and  FK-12-B  breakers  are  being 
superseded  by  the  FK-32-A  and  FK-32-B  standard  unit  designs 
that  can  be  assembled  as  single,  double,  triple,  or  four-pole  com- 
binations. Fig.  69  shows  a  15,000  volt,  800  ampere,  FK-32-B 
breaker  with  tank  lifter  and  one  of  the  tanks  dropped  to  show  the 
type  of  contacts  used. 

The  fixed  contacts  for  the  FK-32-A  breakers  of  400  and  600 
amperes  are  of  wedge  construction,  double  break  per  pole  and 
make  sliding  contacts  under  heavy  pressure  when  the  breaker  is 
closed. 

The  fixed  contacts  for  the  800  and  1200  ampere  FK-32-A 
breakers  and  all  FK-32-B  breakers  are  of  laminated  brush  con- 
struction and  double  break  per  pole.  Wiping  motion  at  closing 
insures  clean  surfaces  on  the  wedge  or  brush  contacts.  With  all 
sizes,  the  arc  is  broken  on  secondary  renewable  contacts  of  copper, 
which  close  and  open  after  the  main  contacts.  The  operating 
mechanism  is  simple  and  positive  in  action,  with  the  breaker 
opening  by  gravity  and  compression  springs.  The  frame  supports 
the  breaker  mechanism  and  the  standard  breaker  units,  each 
with  its  own  tank. 

The  tanks  are  approximately  elliptical  in  cross-section,  of 
heavy  sheet  steel  lined  with  treated  pressboard  to  protect  the 


112        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


tank  against  the  action  of  the  arc.  Strong  supporting  rods 
hook  at  the  bottom  of  the  tank  and,  extending  through  the  cover 
above,  hold  the  tank  firmly. 


ii 


FIG.  69. — General  Electric  Co.  oil  circuit  breaker,  type  FK-32. 

Ratings. — The  rupturing  capacities  assigned  to  the  FK-32-A 
breakers  are  1900  amperes,  at  15,000  volts,  4370  at  7500,  7670  at 
4500,  14,300  at  2500,  while  for  the  FK-32-B  they  are  2900  at 
15,000,  6670  at  7500,  11700  at  4500,  21,800  at  2500  volts. 

Type  K-35.— The  FK-35-Y  and  FK-35  breakers  are  also  built 
on  the  standard  unit  construction,  and  are  intended  for  lower 
voltages  and  lower  currents  than  the  FK-32- A  and  FK-32-B. 
The  rupturing  capacities  assigned  to  the  FK-35  are  2100  at  7500, 
3900  at  4500,  7550  at  2500  and  20,000  at  750  volts. 

The  types  FK-32A  and  FK-32B  oil  circuit  breakers  can  be 
furnished  for  manual  operation  mounted  on  panel,  panel  frame, 
or  remote  on  framework  and  for  solenoid  operation  mounted  on 
framework  or  in  cell. 

Cell  Type. — For  masonry  compartment  mounting,  the  FK-52B 
breaker  as  shown  in  Fig.  70  is  built  for  15,000-volt  service  for 
mounting  on  four-foot  centers  and  for  25,000-volt  service  on  six- 
foot  centers.  Each  unit  is  supported  on  steel  bedplates  in  a  sepa- 


OIL  CIRCUIT  BREAKERS  113 

rate  cell  compartment  and  is  leveled  and  bolted  to  these  plates. 
The  operating  rod  of  each  pole  passes  up  through  the  top  of  the 
cell  and  a  hand  or  solenoid  mechanism  can  be  furnished  for  operat- 
ing all  of  the  poles  at  the  same  time. 


FIG.  70. — General  Electric  Co.  oil  circuit  breaker  type  K-52B. 

The  operating  mechanism  is  designed  to  produce  parallel 
movement  of  blades.  It  has  rustproof  parts  and  noncorrosive 
pins.  The  breaker  opens  by  gravity  assisted  by  springs  on  the 
mechanism.  An  oil  dash  is  used  to  buffer  the  mechanism  at 
the  end  of  the  opening  stroke  and  balancing  springs  help  to 
carry  the  weight  of  the  moving  parts  in  closing.  Provision  is 
made  for  the  insertion  of  a  removable  lever  for  emergency 
operation. 


114        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

The  tanks  are  approximately  elliptical  in  cross-section  and 
are  made  from  heavy  sheet  steel,  acetylene  welded,  and  lined 
with  pressboard.  They  are  supported  from  the  cover  by  bolts, 
which  hook  under  the  bottom  of  the  tank  and  pass  through  the 
cover  where  they  are  securely  fastened.  Oil  gauges  and  gas  vents 
are  provided  for  all  tanks. 

The  bushings  for  15,000  volts  are  of  one-piece  wet-process 
porcelain  extending  below  the  level  of  the  oil.  For  25,000  volts  a 
short  extension  is  clamped  to  the  main  insulator,  thus  giving  the 
contacts  a  greater  depth  in  the  oil. 

The  main  contacts  are  of  laminated  brush  construction  making 
end  contact  with  heavy  and  uniform  pressure,  without  any  ten- 
dency to  force  any  laminations  of  the  brush  apart.  Wiping 
motion  at  closing  keeps  the  contacts  clean. 

Up  to  and  including  1200-ampere  capacity,  round  studs  are 
screwed  and  sweated  into  the  brush  block;  1600-and  2000-ampere 
capacities  have  laminated  studs. 

Ratings. — The  25,000  volt  FK-52-B  have  rupturing  capacities 
of  3450  amperes  at  25,000,  6400  at  15,000  while  the  15,000-volt 
FK-52-B  have  rupturing  capacities  of  5800  at  15,000,  13,350 
at  7500,  23,500  at  4500,  43,500  at  2500  volts. 

Type  H. — The  '  H '  line  of  breakers  covers  the  high  rupturing 
capacity  types  used  principally  in  stations  distributing  at  the 
generator  voltage  and  handling  large  amounts  of  power.  These 
breakers  have  one  tank  per  lead,  six  for  a  3-pole  breaker, 
the  tanks  being  cylindrical  and  normally  located  in  masonry 
compartments.  The  H-l  breaker  was  the  original  pneumatically 
operated  breaker,  the  H-2  was  the  electro-pneumatically  oper- 
ated, the  H-3  was  and  still  is  the  motor  operated  breaker  with 
pots  8  inches  in  diameter,  the  H-4  was  the  high  voltage  design 
of  'H'  construction  using  wooden  pots,  the  H-5  was  a  hand 
operated  breaker.  The  H-6  was,  and  is  the  motor  operated 
with  10-inch  diameter  pots,  and  the  H-9  is  the  motor  operated 
breaker  with  12-inch  diameter  pots. 

Old  Type  H3. — Fig.  71  shows  one  of  the  oil  breakers  supplied 
to  the  generating  stations  and  substations  of  the  New  York 
Central  &  Hudson  River  R.  R.  With  this  type  the  leads 
are  brought  to  the  bottom  of  the  two  metal  tanks  in  each 
compartment,  and  the  circuit  is  completed  through  the 
plunger  rods  that  pass  through  insulated  bushings  in  the 
top  of  the  tanks.  These  rods  are  connected  together  by 


OIL  CIRCUIT  BREAKERS 


115 


metal  crosspieces,  and  where  the  amount  of  current  exceeds 
that  which  the  plunger  rods  can  carry,  laminated  copper 
brushes  are  used  for  bridging  across  between  the  pots.  The 
brushes  and  plungers  are  lifted  by  means  of  wooden  rods,  oper- 
ated by  a  motor  driven  mechanism  located  at  the  top  of  the 
breaker.  Each  pole  of  the  breaker  is  installed  in  separate 
masonry  compartments,  and  fireproof  doors  are  used  for  closing 


FIG.  71. — General  Electric  Co.  oil  cir- 
cuit breaker  type  H3. 


FIG.  72. 


in  the  compartments.  This  style  of  breaker  is  very  compact  and 
is  particularly  well  suited  for  connecting  to  busbars,  located 
directly  below  the  breaker  on  a  lower  gallery. 

For  larger  currents,  where  the  plunger  contacts  cannot  readily 
take  care  of  the  amount  of  current  to  be  handled,  auxiliary  con- 
ducting bars  are  run  outside  of  the  pots  from  the  bottom  contact, 
attached  to  insulator,  to  the  top,  where  plates  are  placed  on  the 
tanks  and  brushes  span  across  between  the  two  tanks  of  the 
same  phase. 

Tank  Section. — Fig.  72  shows  a  sectional  view  through  a 
tank  of  an  H-3  breaker  in  the  open  position  with  the  plunger  rod 


116        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


withdrawn  to  the  extreme  limit  of  the  stroke.  In  the  closed 
position  the  tip  of  the  plunger  rod  engages  with  the  stationary 
contacts  at  the  extreme  bottom  of  the  tank  and  has  a  fairly  long 
bearing  surface  to  secure  self-cleaning  action  between  the  moving 
rod  and  the  stationary  contacts.  A  baffle  plate  is  provided 
about  half  way  through  the  oil  and  about  40  per  cent,  of  the  space 

in  the  top  of  the  tank  is  left 
available  as  an  air  compression 
chamber  to  take  up  the  shock 
of  the  explosion  when  opening 
under  load. 

The  cut  represents  what  is 
supposed  to  happen  in  the  tank 
at  the  instant  of  opening  under 
load.  The  arc  has  a  tendency 
to  follow  after  the  moving  con- 
tact and  a  gas  bubble  is  formed 
that  is  largely  prevented  from 
following  after  the  moving  con- 
tact by  the  action  of  the  baffle 
plate.  This  minimizes  the  dis- 
turbance of  the  oil  in  the  upper 
part  of  the  tank. 

By  the  adoption  of  the  de- 
mountable type  of  tank  con- 
struction shown  in  Fig.  73  the 
time  needed  for  taking  down  a 
tank  is  reduced  to  a  minimum 
and  by  keeping  a  few  spare 
poles  available  a  new  one  can 
be  quickly  substituted  and  the 
replaced  one  examined  when  a 
suitable  opportunity  arrived. 

This  same  feature  has  been 

embodied  in  the  H-6  and  H-9  types  of  breakers  to  gain  the 
same  advantages. 

Type  H-6. — To  secure  greater  rupturing  capacities  than  could 
be  obtained  in  the  8-inch  pots  of  the  H-3  breakers,  the  H-6  line 
of  breakers  was  brought  out  with  10-inch  diameter  pots  and  these 
in  turn  have  been  followed  by  the  H-9  line  of  breakers  with  12- 


FIG.  73. 


OIL  CIRCUIT  BREAKERS 


117 


inch  pots.     Still  larger  pots  can  be  supplied  if  necessary,  or  two 

or  more  pots  used  in  series  to  obtain  greater  rupturing  capacity. 

Fig.  74  shows  a  type  H-6  breaker,  1200  amperes,  15,000  volts, 

with  the  parallel  arrangement  of  tanks.     This  is  the  manner  in 


FIG.  74. — General  Electric  Co.  oil  circuit  breaker  type  H6  with  parallel  pots. 

which  the  breaker  is  normally  arranged,  but  for  certain  conditions 
such  as  for  bus  sectionalizing  circuits,  the  tandem  arrangement  of 
pots  as  show  in  Fig.  75  works  out  to  advantage. 

These  breakers  are  usually  made  bottom  connected  but  the 
parallel  pot  breakers  can  easily  be  arranged  with  the  rear  tanks 
top  connected.  With  the  tandem  pots,  all  can  be  made  top  con- 
nected if  this  best  works  into  the  scheme  of  wiring. 

With  the  H-9  breakers  in  a  recent  installation  the  position  of 
the  pots  was  a  compromise  between  the  parallel  pot  and  the 
tandem  and  might  be  described  as  the  staggered  pot  arrange- 


118        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


ment.  The  pots  were  all  top  connected  and  the  front  pots  were 
sufficiently  to  one  side  of  the  rear  pots  that  the  leads  could  be 
run  straight  back  without  any  interference.  Other  modifica- 
tions of  the  *H'  line  of  breakers  can  be  made  to  meet  local  con- 
ditions. 


FIG.  75. — General  Electric  Co.  oil  circuit  breaker  type  H6  with  tandem  pots. 

Mechanisms. — The  mechanisms  for  the  types  FH-3  and  FH-6 
oil  circuit  breakers  have  the  following  features: 

Speed. — The  contacts  part  in  0.2  seconds  after  contacts  of  over- 
load relay  or  control  switch  close,  and  the  switch  is  completely 
opened  in  0.59  seconds.  A  complete  cycle,  opening  and  closing 
can  be  accomplished  in  2  seconds.  Torsion  springs  counter- 
balance the  weight  of  the  mechanism,  making  equally  rapid 
motion  for  either  stroke. 

Compression  springs  throw  the  breaker  about  1  inch  into  con- 
tact on  closing  and  about  1^  inches  from  full  stroke  on  opening, 
both  with  a  rapid  movement.  The  stroke  is  completed  by  the 


OIL  CIRCUIT  BREAKERS  119 

motor.  The  motor  completes  the  stroke  begun  by  the  compres- 
sion springs  and  compresses  the  operating  springs  at  the  end  of 
each  stroke  (either  opening  or  closing),  thereby  preparing  the 
breaker  for  the  reverse  operation. 

The  master  finger  closes  a  circuit  paralleling  the  safety  switch 
at  the  first  movement  of  the  switch  mechanism,  thereby  insuring 
the  completion  of  the  operation. 

The  magnetic  clutch  disconnects  the  motor  from  the  mechan- 
ism when  not  needed,  preventing  injury  to  the  motor  by  sudden 
stopping  of  the  mechanism. 

Ratings. — The  rupturing  capacity  assigned  to  these  breakers 
is  as  follows: 

Volts  2,500  4,500  7,500  15,000 

H-3  Amperes 75,000  40,300  23,000  10,000 

H-6  Amperes 135,000  72,600  41,400  18,000 

H-9  Amperes.....  150,000  92,700  52,900  23,000 

For  the  smaller  current  ratings  at  the  lower  voltages  the  ratings 
are  limited  to  100  times  the  normal  ratings  of  the  breakers  as  the 
carrying  capacities  of  the  contacts  are  the  limiting  features. 

High  Voltage  Breakers. — All  of  the  high  voltage  breakers  of 
the  General  Electric  Company  now  in  standard  production  are  of 
the  'K'  lines  with  various  sub-number  designations,  the  numerals 
such  as  24,  26,  36,  etc.,  being  followed  by  the  letter  'O '  where  the 
breakers  are  used  for  outdoor  service.  These  breakers  are  built 
for  pipe  frame  mounting  up  to  50,000  volts,  for  structural  frame 
mounting  for  73,000  volts  and  for  platform  mounting  for  higher 
voltages. 

Type  FK-24.— Fig.  76  shows  a  15,000-volt  500-ampere  FK-24 
breaker  for  indoor  service.  Each  pole  is  in  a  separate  steel  tank, 
the  individual  tanks  being  on  a  common  frame  and  operated  by 
a  common  mechanism  that  is  designed  to  produce  parallel  move- 
ment of  the  blades.  This  mechanism  has  rust  proof  parts  and 
noncorrosive  pins.  Provision  is  made  in  the  mechanism  for 
insertion  of  a  removable  hand-closing  lever.  Where  space  is 
'  limited,  the  breaker  can  be  furnished  with  a  one-piece  top,  sup- 
porting all  of  the  elements. 

Hung  'from  the  top  are  the  tanks  of  heavy  sheet  steel,  acetylene 
welded,  with  separate  tank  for  each  pole,  and  oil  gauges  for 
each  tank.  The  bushings  are  one-piece  porcelain  made  by  the 
wet  process  and  extending  below  the  level  of  the  oil.  These 


120        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


bushings  are  held  in  clamps  with  interchangeable  metal  plates 
with  trued  surfaces  to  get  proper  alignment  and  to  facilitate  re- 
moval-and  inspection. 

The  fixed  contacts  are  made  of  forged  copper  fingers  at  the  end 
of  the  terminal  studs  that  pass  through  the  bushings.  The 
fingers  are  flared  at  the  tips  and  one  set  is  extended  to  act  as 


FIG.  76. — General  Electric  Co.  oil  circuit  breaker  type  FK24. 

arcing  tips.  The  movable  contact  blade  is  screwed  and  clamped 
to  the  operating  rod.  The  contacts  are  wedge-shaped  which 
confines  the  arc  to  their  top  edge  and  to  the  flared  portion  of  the 
finger  tips. 

Ratings.— The  rupturing  capacities  of  the  35,000-volt  FK-24 
breaker  is  1100  amperes  at  35,000  volts;  1670  at  25,000;  for  the 
25,000-volt  breaker  1500  at  25,000;  2800  at  15,000  and  for  the 
15,000-volt  breaker  2500  at  15,000,  5750  at  7500. 

Type  FK-26.— Fig.  77  shows  a  frame  mounted  FK-26  breaker 
for  indoor  service  at  45,000  volts.  Most  of  its  features  corre- 
spond with  those  of  the  FK-24  previously  described,  but  the 


OIL  CIRCUIT  BREAKERS 


121 


general  dimensions  are  considerably  larger  and  the  bushings 
instead  of  being  of  the  porcelain  type  are  of  built  up  material 
with  a  contact  tube  extending  through  it  and  binding  together 
the  upper  and  lower  sections.  A  maple  cover  keeps  out  dirt  and 
protects  the  end  of  the  bushing.  Porcelain  ends  prevent  injury 
to  the  bushing  by  any  arc  or  discharge  that  might  occur. 


FIG.  77. — General  Electric  Co.  oil  circuit  breaker  type  K26. 

The  interior  of  the  45,000-volt  bushing  has  the  contact  tube 
surrounded  by  an  insulating  material  and  the  bushing  filled  with 
an  insulating  compound  of  high  dielectric  strength.  The  bush- 
ing for  70,000-volt  service  has  a  set  of  cylinders  of  insulating 
material  concentric  with  the  contact  tube,  the  whole  being  filled 
with  an  insulating  compound.  At  the  bottom  of  the  70,000- 


122        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


volt  bushing  that  is  under  the  oil  a  static  shield  is  provided  that 
partly  surrounds  the  contacts. 

Type  FKO-26.— Fig.  78  shows  the  FKO-26  breaker  for  frame 
mounting  outdoor  service,  this  differing  principally  from  the 
indoor  type  in  the  waterproof  covering  for  the  operating  mechan- 
ism and  the  porcelain  rain  shields  over  the  portions  of  the  bush- 
ings that  are  exposed  to  the  weather.  With  all  of  these  breakers, 


FIG.  78. — General  Electric  Co.  oil  circuit  breaker  type  K026. 

the  cast-iron  support  built  into  the  bushing  serves  as  the  means  of 
attaching  it  to  the  breaker.  Where  bushing  transformers  are 
used,  this  cast-iron  housing  is  made  large  enough  to  house  and 
protect  them. 

These  breakers  can  be  supplied  for  floor  mounting  or  for  frame 
mounting.  The  framework  for  the  50,000-volt  breaker  is  made 
of  pipe  while  that  for  the  73,000  is  made  principally  of  channel 
irons. 

The  rupturing  capacities  for  the  70,000-volt  breakers  are  1950 
amperes  at  70,000  volts;  2200  at  50,000;  2500  at  45,000;  3130  at 


OIL  CIRCUIT  BREAKERS 


123 


37,000  and  for  the  45,000,  1600  at  45,000;  2050  at  37,000  and  3260 
at  25,000. 

Type    FKO-36.— Fig.    79  shows  a  floor  mounting  FKO-36 
for  outdoor  service,  this  breaker  having  a  guaranteed  rupturing 


-.1 


FIG.  79. — General  Electric  Co.  oil  circuit  breaker  type  K036. 

capacity  of  3290  amperes  at  110,000  volts.  The  sides  of  this 
tank  are  practically  flat  but  the  arc  is  broken  under  the  oil  in  a 
special  explosion  chamber  shown  in  Fig.  80. 


Fia.    80. — General    Electric    Co.    oil    circuit    breaker    type    K036.     Explosion 
chamber. 

The  function  of  this  explosion  chamber  is  based  on  the  theory 
that  by  confining  the  arc  to  a  largely  restricted  space  a  high 
pressure  will  be  developed  tending  to  blow  the  arc  away  from 
the  contact  causing  its  rapid  extinction.  The  steel  cylinder 
forming  the  explosion  chamber  can  be  readily  made  of  ample 
strength  for  the  pressure  developed. 


124        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Ratings. — The  FK-36 '  and  FKO-36  are  built  with  various 
sized  tanks  and  given  varying  rupturing  capacity  ratings.  For 
example  at  155  K.V.  breakers  are  available  with  rupturing  capa- 
city ratings  of  900,  2300  and  3500  amperes;  for  135  K.V.  the 
ratings  are  from  950  to  3600  amperes;  for  115  K.V.  from  1000 
to  4400  amperes,  etc. 

Modifications  of  these  breakers  are  available  and  in  services 
up  to  160,000  volts  and  designs  have  been  made  for  service  at 
220,000  volts  and  such  breakers  are  now  being  built  for 
California. 

WESTINGHOUSE  OIL  CIRCUIT  BREAKERS 

While  the  Westinghouse  Company  had  made  oil  switches  and 
oil  circuit  breakers  in  various  forms  prior  to  1904,  their  annual 
catalogue  of  that  year  was  their  first  one  with  various  lines  of  oil 
circuit  breakers  and  switches  listed  and  described  in  it.  At  that 
time  the  term  oil  switch  was  applied  to  those  pieces  of  apparatus 
in  which  the  contacts  were  of  the  knife  type  that  did  not  have 
any  tendency  to  come  open  and  the  term  oil  circuit  breaker  was 
applied  to  those  pieces  of  apparatus  so  designed  that  the  con- 
tacts tend  to  separate  and  were  only  held  in  the  closed  position 
by  means  of  triggers  and  toggles. 

In  the  descriptions  that  follow,  the  oil  circuit  breakers  are 
taken  up  about  in  the  order  of  their  rupturing  capacity  in  place 
of  alphabetically  by  type  letters. 

Knife  Contacts. — Type  I  oil  circuit  breakers,  manually  oper- 
ated, non-automatic,  for  indoor  service,  single  and  double 
throw,  are  made  for  capacities  up  to  60  amperes  4500,  volts  A.C., 
interrupting  capacity  at  rated  voltage,  300  amperes.  The 
characteristic  features  of  the  type  I  oil  circuit  breakers  are:  knife 
blade  contacts  submerged  in  oil;  live  parts  carried  on  porce- 
lain base  affording  high  quality  of  permanent  insulation  between 
adjacent  poles,  and  between  frame  and  live  parts;  small  space 
required  for  mounting;  light  weight;  tanks  removable  without 
disturbing  contacts,  making  easy  accessibility  of  parts  for  purpose 
of  inspection  and  repairs;  enclosure  of  all  live  parts;  and  low  first 
cost.  The  breaker  is  essentially  a  knife  switch  submerged  in  oil 
and  arranged  for  external  operation. 

Type  D. — Type  D  oil  circuit  breakers  are  manually  operated 
non-automatic  made  for  indoor,  outdoor  and  subway  service, 
single  and  double  throw,  for  capacities  up  to  300  amperes,  1500 


OIL  CIRCUIT  BREAKERS  125 

volts,  200  amperes,  4500  volts,  alternating  current,  interrupting 
capacities  at  rated  voltage  700  to  800  amperes. 

These  non-automatic  oil  circuit  breakers  have  a  wide  range  of 
application,  being  made  for  indoor  service  in  panel  mount- 
ing, direct  wall-mounting,  remote-control  wall  or  pipe  mount- 
ing, and  for  subway  mounting. 

Outdoor  Type. — The  outdoor  form  of  wall  or  pole  mounting 
breaker  is  primarily  intended  for  service  in  exposed  places. 

The  wall  or  pole  mounting  breaker  is  enclosed  in  a  weather- 
proof case  having  lugs  cast  thereon  for  mounting  the  breaker  on 
a  wall  or  pole.  On  these  outdoor  breakers  a  crank  handle  is  used 
for  operation.  The  leads  are  brought  out  underneath  the  top 
part  of  the  case,  through  sealed  bushings  at  the  side  and  under- 
neath the  main  casting.  The  sealing-in  of  the  bushings  prevents 
the  entrance  of  rain  or  moisture  to  the  interior  of  the  breaker. 

Subway. — The  subway  form  of  breaker  is  intended  for  mount- 
ing in  subways,  manholes,  or  other  places  where  a  breaker  may 
be  required  to  operate  submerged.  This  subway  form  of  breaker 
is  made  in  2,  3  or  4-pole,  single  and  double  throw,  for  capacities 
up  to  200  amperes,  4500  volts. 

The  housing  for  the  subway  breaker  complete,  including  the 
oil  tank,  is  of  cast  iron.  All  housing  joints  are  made  water- 
proof by  the  use  of  gaskets.  The  housing  has  lugs  cast  thereon 
for  mounting  the  breaker  on  the  wall  of  the  subway,  manhole 
or  other  place  of  mounting. 

The  leads  enter  the  breaker  housing  through  individual  water- 
proof bushings  in  the  top  of  the  case.  The  operating  handle  is 
provided  with  a  waterproof  stuffing  box  and  is  latched  in  either 
the  "on"  or  "off"  position. 

Features. — The  characteristic  features  of  the  type  D  oil 
circuit  breakers  are:  knife  blade  contacts  submerged  in  oil  and 
protected  by  auxiliary  arcing  contacts;  live  parts  carried  on  in- 
sulating supports  affording  a  high  quality  of  permanent  insulation 
between  adjacent  poles,  and  between  the  frame  and  live  parts; 
all  parts  supported  by  a  single  frame  easily  mounted  on  panel, 
wall,  pipe  frame,  post,  bracket,  or  other  vertical  support;  small 
space  required  for  mounting;  accessibility  of  parts  for  the  pur- 
pose of  inspection  and  repair;  enclosure  of  all  live  metal  parts; 
simple  but  rugged  construction. 

Tanks. — The  oil  tanks  are  rectangular  in  shape  and  are  made 
of  heavy  sheet  iron.  Individual  insulating  cells  on  single-throw 


126        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

breakers,  and  an  insulating  lining  on  double-throw  breakers,  are 
used  as  an  additional  protection  against  arcing  from  current- 
carrying  parts  to  the  metal  of  the  tank.  Where  the  individual 
insulating  cells  are  used  on  the  single-throw  breakers,  they  form 
a  separate  compartment  for  each  pole.  While  the  tank  is 
securely  fastened  to  the  breaker  frame,  the  construction  permits 
of  easy  removal  for  the  purpose  of  inspection  and  repair. 

The  tanks  are  deep  to  allow  ample  space  above  the  oil  level 
to  act  as  an  expansion  chamber  for  the  arc  gases,  and  to  reduce 
slopping  of  the  oil  from  internal  disturbances.  The  gases  are 
vented  through  the  clearance  between  the  wooden  operating 
rod  and  the  frame. 

Type  F. — Type  F  oil  circuit  breakers  are  made  manually 
and  electrically  operated,  non-automatic  and  automatic,  for 
indoor  and  outdoor  service,  single  and  double  throw,  for  capaci- 
ties up  to  3000  amperes,  13,200  volts  A.C.,  interrupting  capaci- 
ties at  rated  voltage,  1000  to  15,000  amperes. 

These  type  F  oil  circuit  breakers  comprise  a  complete  line 
of  moderate-capacity,  non-automatic  and  automatic,  manually 
and  electrically  operated  breakers.  For  indoor  service,  the 
breakers  are  made  in  the  panel  mounting,  and  remote-control  wall 
or  pipe  mounting  forms,  and  for  outdoor  service  in  pole  or  sub- 
way mounting  forms. 

Among  the  features  of  the  type  F  breakers  are:  Wedge  and 
finger-type  contacts.  Auxiliary  arcing  contacts.  Submersion 
and  opening  of  all  contacts  under  oil.  Quick  opening  of  contacts, 
assisted  by  arcing  tip  springs.  Open  position  maintained  by 
gravity.  Inability  to  hold  full  automatic  breaker  in  the  closed 
position  when  an  excessive  overload  or  short  circuit  exists  on  the 
line.  Strong  tanks  and  tank  supports.  Tanks  removable  with- 
out disturbing  the  operating  mechanism  or  contacts,  making  in- 
spection easy.  Ample  air  space  at  the  top  of  the  tank  to  allow 
for  gas  expansion.  Insulating  lining  in  the  tanks.  Isolation  of 
poles  by  individual  cells.  Self  contained  rnultipole  hand-  or  elec- 
tric-operating mechanism  on  the  multipole  single-tank  breakers. 

The  type  F  oil  circuit  breakers  are  made  non-automatic 
and  full-automatic,  direct  or  remote-control  manually  operated; 
and  non-automatic  and  automatic  electrically  operated. 

Type  F-l. — Fig.  81,  shows  a  type  F-l  indoor  manually 
operated  remote-control  pipe  mounting  three-pole  single-throw 
200-ampere,  4500-volt  breaker  with  micarta  tubes  over  terminals 


OIL  CIRCUIT  BREAKERS  127 

and  with  tank  removed.  The  standard  overload-trip  .range  of 
these  breakers  is  80  to  160  per  cent,  of  the  normal  full-load  cur- 
rent rating  or  primary  rating  of  the  current  transformer  in  the 
trip  coil  circuit. 


FIG.  81. — Westinghouse  oil  circuit  breaker,  type  F-l. 

Transformer  Trip. — For  this  method,  type  F  automatic 
breakers  are  made  with  trip  coils  mounted  on  the  coverplate  of 
hand  operated  breakers  or  on  the  electric  mechanism  of  electri- 
cally operated  breakers.  A  single  5-ampere  coil  is  regularly 
used  on  single  pole  and  2-pole  breakers,  and  two  5-ampere 
coils  on  3-pole  and  4-pole  breakers.  For  use  on  2-phase  or 
3-phase,  where  accurate  overload  tripping  is  not  required  on 
a  single-phase  overload  or  short  circuit,  single  coil  3-  and 
4-pole  breakers  having  only  one  special  8.7-ampere  overload 
trip  coil,  are  obtainable.  This  special  trip  coil  can  be  con- 
nected to  two  current  transformers  in  "vector  parallel,"  in 
which  case  the  single-phase  overload  accuracy  is  within  good 
operating  limits  of  the  polyphase  calibration. 

Series  Trip. — For  series  tripping,  type  F  indoor  breakers 
are  made  with  alternating-current  series-overload  trip  coils 
mounted  in  the  switchboard  cover  plate  dry  insulated,  for 
voltages  up  to  2500  and  capacities  from  10  to  300  amperes. 

Multiple -Multipole. — Multipole  breakers  having  a  single 
mechanism  and  tank  are  made  up  to  maximum  capacities  of  800 


128        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

amperes.  In  addition,  type  F-3  breakers,  either  manually  or 
electrically  operated  remote  control,  can  be  supplied  in  capacities 
up  to  3000  amperes  by  using  3  or  4-pole  standard  units  with 
the  contacts  connected  in  multiple  for  each  pole,  (multiple-multi- 
pole).  Type  F-3  breaker  frames  are  specially  designed  for  this 
purpose. 

Manual  Operation. — Manually  operated  direct  control  break- 
ers are  made  either  for  panel  or  panel-frame  mounting,  or  for 
remote  control  wall  or  pipe  mounting.  The  type  F-2  multiple 
single-pole  wall  mounting  breakers  (a  multipole  breaker  made 
up  of  single  pole  units)  and  the  type  F-3  multiple-multipole  wall 
mounting  breakers  (a  multipole  breaker  made  up  of  standard 
remote  control  3  or  4-pole  units  to  form  one  high  capacity 
multipole  breaker)  when  equipped  with  appropriate  fittings,  can 
be  used  for  cell  mounting,  erected  in  brick,  asbestos  lumber,  or 
concrete  structure,  with  each  pole  enclosed  in  a  separate  com- 
partment. 

Electrical  Operation. — Electrically  operated  multipole  single- 
tank  breakers  are  made  with  self-contained  mechanisms  for 
either  wall  or  pipe  mounting.  The  multiple  single-pole  electric- 
ally operated  breakers  are  made  for  either  wall  or  pipe  mounting 
with  separate  operating  mechanisms  placed  above,  below,  or 
behind  the  breaker,  while  the  electric  operating  mechanism  of  the 
multiple-multipole  breakers  can  be  mounted  only  below  the 
breaker. 

Tanks. — Multipole  single  tank  construction  is  used  on  all 
type  'F1  breakers,  except  the  type  F-2  multiple  single-pole,  and 
the  type  F-3  multiple-multipole,  which  use  one  tank  per  pole. 
The  oil  tanks  are  rectangular  in  shape  and  are  made  of  heavy 
sheet-iron  with  all  seams  lap-welded,  the  bottom  being  flanged 
and  welded  on  the  outside  of  the  tank  sides.  As  an  additional 
protection  from  arcing,  individual  insulating  cells  form  separate 
compartments  for  each  pole  where  one  tank  is  used  on  multipole 
breakers. 

Studs. — The  terminal  studs  or  bushings  with  stationary 
contacts  or  feet  on  the  lower  extremity  are  supported  by  one- 
piece  vertical  pillar  type  porcelain  bushings  clamped  to  the 
framework.  The  studs  and  micarta-tube  details  are  clamped  to 
these  insulators.  This  construction  avoids  the  use  of  babbitt 
and  cement,  thus  reducing  the  time  and  labor  of  maintenance. 


OIL  CIRCUIT  BREAKERS  129 

Contacts. — The  main  moving  contacts  are  wedge  type.  The 
main  stationary  contacts  consist  of  fingers  of  the  "controller" 
type  arranged  in  pairs  facing  each  other  so  as  to  make  perfect 
contact  on  the  two  surfaces  of  the  moving  contact  wedge  when 
the  breaker  is  closed.  The  contact  tips  on  the  end  of  the  fingers 
are  supported  on  the  ends  of  thin  flat  steel  springs,  permitting  the 
contact  to  move  in  all  directions  and  to  automatically  align  itself 
on  the  wedge,  thus  insuring  that  the  full  carrying  capacity  of  the 
contacts  is  always  available.  This  spring  is  shunted  by  a  liberal 
copper-leaf  shunt  to  conduct  the  current  from  the  tips  to  the 
terminal  stud. 

Arcing  Contacts. — These  are  made  of  the  butt  type  to  protect 
the  main  contacts  from  the  action  of  arcs  at  breaking.  The 
stationary  member  consists  of  a  spring  plunger  and  copper 
arcing  tip  mounted  on  the  support  of  the  main  contact.  A  flex- 
ible copper  wire  shunt  carries  the  current  from  the  stud  to  this 
tip.  A  copper  bolt  is  carried  on  the  conducting  cross-bar  of  the 
moving  contact  element  and  serves  as  the  moving  arcing  contact. 
The  auxiliary  arcing  contacts  maintain  contact  for  a  considerable 
distance  after  the  main  contact  fingers  have  broken  contact. 
This  time  interval  is  predetermined  by  the  amount  of  separation 
of  the  main  contact  fingers  produced  by  the  steel  stop  and  serves 
to  fully  protect  the  main  contacts. 

Type  H. — These  oil  circuit  breakers  are  small  capacity  manu- 
ally operated  single-throw  breakers  for  indoor  use  (dust-proof 
wall  mounting)  and  outdoor  use  (weatherproof,  wall  or  pole 
mounting).  These  breakers  supply  the  need  for  a  simple, 
reliable,  inexpensive  oil  circuit  breaker  for  use  in  general  indus- 
trial applications.  They  are  particularly  useful  for  controlling 
motor  circuits,  or  other  loads  of  low  power  factor,  where  exces- 
sive arcing  would  occur  when  using  an  air-break  switch  at  low 
power  factor,  thus  making  the  use  of  an  oil  circuit  breaker 
advisable.  The  cylindrical-rod  butt-type  contact  is  used.  The 
contacts  consist  of  cylindrical  rods,  the  lower  one  backed  by 
spiral  springs  to  insure  contact.  This  type  of  contact  is  used 
on  the  multiple  unit  control  system  of  heavy  street-railway 
equipment  and  has  been  adapted  with  great  success  to  oil  cir- 
cuit breaker  practices.  It  insures  good  contact  at  all  times,  and 
prevents  any  possible  failure  due  to  the  eating  away  of  the  con- 
tact by  continued  arcing.  The  compression  springs  take  up  any 


130        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

wear  that  may  occur.     The  contacts  have  long  life,  and  are 
readily  removed  and  replaced  when  necessary. 

Type  QF. — The  type  'QF'  motor  starting  oil  circuit  breakers 
shown  in  Fig.  82,  are  especially  designed  for  starting,  in  connec- 
tion with  auto  transformers,  3  phase  squirrel-cage  induction 
and  self-starting  synchronous  motors  up  to  720  H.P.  When 
properly  applied  they  protect  the  motor  in  the  running  position 
from  heavy  overloads  and  short  circuits,  and  guard  it  against 
the  sudden  application  of  full  voltage  to  the  motor  after  it  has 
slowed  down  or  come  to  rest  following  an  interruption  of  power. 


FIG.  82. — Westinghouse  type  "QF"  Motor  starting  oil  circuit  breaker. 

The  type  QF  motor  starting  oil  circuit  breaker  is  a  double- 
throw  breaker  with  special  moving  and  stationary  contact 
arrangement.  In  effect,  it  is  a  3-pole,  double-throw  breaker 
with  three  additional  terminals  used  to  complete  the  auto- 
transformer  circuits  when  the  breaker  is  in  a  starting  position. 
The  auto  transformers  are  mounted  separately  from  the  breakers. 
The  tap  leads  of  the  transformers  are  permanently  connected 
to  the  motor  leads. 

Type  B. — The  modern  type  'B'  oil  circuit  breakers  comprise  a 
line  of  medium  capacity  breakers  built  of  three  different  forms, 
namely,  types  'BA,'  'B-2/  and  'B-13/  each  with  a  different 
interrupting  capacity,  different  maximum  voltage  and  details  of 
construction. 

These  breakers  have  a  wiping  and  self-cleaning  form  of  lami- 


OIL  CIRCUIT  BREAKERS 


131 


nated  brush  contact,  protected  by  butt  arcing  contacts.  The 
opening  of  all  contacts  occurs  under  oil  with  a  positive  direct 
gravity  break  assisted  by  spring  acceleration,  and  with  open 
position  maintained  by  gravity.  The  type  'B'  circuit  breaker 
is  in  general  a  common-frame  circuit  breaker.  The  type  'B-A' 
has  a  tank  per  pole  in  all  sizes.  The  type  'B-2'  has  a  tank  per 
pole  in  the  300-ampere  and  600-ampere  sizes,  but  a  single  tank 
construction  in  the  other  sizes.  The  type  'B-13'  has  a  tank 
per  pole  in  all  sizes. 


FIG.  83.— Westinghouse  type  "BA"  oil  circuit  breaker,  300  amps.,   15  K.V. 


Manually  operated  circuit  breakers  are  actuated  by  a  handle 
mounted  in  the  switchboard  cover  plate.  When  the  breakers  are 
supplied  with  automatic  overload  trip  with  remote  control,  an 
accelerating  spring  device  is  used  to  quicken  the  opening  of  the 
contacts,  and  this  device,  assisted  by  the  arcing  contact  springs, 
gives  to  the  moving  parts  an  acceleration  greater  than  that  caused 
by  gravity. 

Fig.  83  shows  a  4-pole  300-ampere,  15,000  volt  'BA' 
oil  circuit  breaker  with  one  tank  removed,  showing  contact 
details  on  one  pole.  Fig.  84  shows  a  3-pole-solenoid  operated 


132        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


'B-13'  breaker  600  amperes  25,000  volts  arranged  for  pipe  frame 
mounting.  All  of  the  following  sizes  of  circuit  breakers  can  be 
supplied  either  manually  or  electrically  operated  and  either  auto- 
matic with  transformer  trip  coils  or  non-automatic.  The  manu- 


FIG.  84. — Westinghouse  oil  circuit  breaker  type  B13. 

ally  operated  breakers  can  be  panel  or  panel  frame  mounting  or 
remote  control,  while  the  remote- control  breakers,  both  hand  and 
electrically  operated,  can  be  furnished  for  wall  mounting  or  pipe 
frame  mounting.  All  can  be  furnished  in  2,  3  or  4-pole  types. 


Maximum 

Amperes 

Interrupting 
capacity 

T\/f 

- 

Type 

ivi  a  xim  u  ni 
volts 

in  arc 
amperes 

60  cycle 

25  cycle 

at  rated 

voltage 

BA  

300 

400 

15,000 

1,350 

BA  

600 

750 

7,500 

3,500 

B-2  

300 

400 

15,000 

1,900 

B-2  

300 

400 

25,000 

960 

B-2  

600 

750 

15,000 

1,900 

B-2  

600 

750 

25,000 

960 

B-2  

1,200 

1,350 

15,000 

1,900 

B-2  

1,500 

1,750 

7,500 

3,000 

B-2  

1,750 

2,000 

7,500 

3,000 

B-2    

2,000 

2,250 

7,500 

3,000 

B-13  

300 

400 

25,000 

l',630 

B-13 

600 

750 

25,000 

1,630 

B-13. 

1,200 

1,350 

15,000 

3,400 

OIL  CIRCUIT  BREAKERS  133 

Multiple-Multipole. — These  type  B  oil  circuit  breakers  can  be 
furnished  for  applications  requiring  a  breaker  having  current 
carrying  capacities  up  to  6000  amperes,  60  cycles.  As  indicated 
by  their  name,  these  breakers  consist  of  a  number  of  multipole 
single  frame  breaker  units,  each  unit  having  its  poles  connected 
in  multiple  to  serve  as  one  phase  leg.  All  phase  leg  units  are 
operated  simultaneously  by  means  of  a  common  operating 
shaft  and  bell  cranks.  For  example,  a  4800-ampere  3-pole  type 
B-2  multiple-multipole  breaker  consists  of  three  2000-ampere,  3- 
pole  units.  The  poles  of  each  3-pole  unit  are  connected  in 
parallel,  thereby  forming  one  4800-ampere  pole.  Three  such 
poles  units  operated  simultaneously  meet  all  the  requirements  of 
a  4800-ampere  8- pole  breaker. 

Connections. — In  making  connections  to  a  multiple  -multipole 
breaker  care  must  be  exercised  not  to  "bus"  the  connections  at 
the  breaker  studs  on  both  sides.  If  this  is  done  the  contact 
resistance  of  the  connections  is  the  only  source  of  voltage  drop. 
Thus  a  slight  increase  in  contact  resistance  on  one  stud  of  a 
"bussed"  connection  results  in  the  other  studs  in  the  same  paral- 
lel circuit  taking  more  than  their  share  of  the  current,  heating 
develops  and  then  the  results  are  cumulative.  Any  difficulties 
from  such  a  source  can  be  overcome  by  using  cables  to  connect 
to  the  breaker  on  at  least  one  side.  The  number  of  cables  should 
be  the  same  as  the  number  of  parallel  circuits  through  the  breaker 
or  multiples  thereof.  The  resistance  of  the  relatively  long  cable 
connections  is  such  that  even  a  100  per  cent,  change  in  the  contact 
resistance  at  one  stud  would  be  but  a  small  percentage  change  in 
the  total  resistance  of  the  total  parallel  circuit  and  no  uneven 
distribution  of  the  current  results. 

Mounting. — The  type  B  breakers  are  arranged  for  either 
panel,  panel  frame  or  pipe  frame  mounting  direct-control;  and  in 
the  remote-control  form,  for  wall  or  pipe  frame  mounting.  The 
remote-control  breakers  can  be  mounted  in  cells,  the  single  frame 
circuit  breakers  being  mounted  as  a  unit  in  one  cell,  which  can  be 
made  of  brick,  asbestos  lumber,  or  concrete. 

Tanks. — These  are  rectangular  in  shape  except  on  the  1200 
ampere  and  2000-ampere  type  B-13  breakers  which  have  elliptical 
tanks  similar  to  those  supplied  on  the  type  E  line  of  breakers. 
The  tanks  are  made  of  heavy  sheet-iron,  with  all  seams  lap- 
welded,  the  bottom  being  flanged  and  welded  on  the  outside  of 
the  tank  sides.  The  tanks  have  a  micarta  lining,  and  where  one 


134        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

tank  is  used  on  multipole  circuit  breakers,  individual  insulating 
cells  form  separate  compartments  per  pole. 

The  tanks  are  especially  deep  to  give  a  large  head  of  oil  over 
the  contacts,  to  allow  ample  space  above  the  oil  level  to  act 
as  an  expansion  chamber  for  the  arc  gases,  and  to  reduce  spilling 
of  the  oil  from  the  internal  disturbances.  On  the  type  B-A  and  B-2 
circuit  breakers,  the  gases  are  vented  around  the  lifting  rod. 
The  type  B-13  circuit  breakers  are  equipped  with  specially 
designed  baffled  vents. 

Moving  Contacts. — The  main  moving  contacts  are  of  the 
laminated  butt  brush  type.  When  the  high  contact  pressure 
used  is  imposed  on  the  movable  contact  (the  butt  brush),  its 
contact  surface  spreads  out  on  the  stationary  contact  (a  plane 
surface)  producing  a  wiping  action  which  automatically  cleans 
both  the  stationary  and  moving  contact  faces. 

Stationary  Contacts. — The  stationary  contacts  are  mounted  on 
the  lower  end  of  the  terminal  studs  and  provide  a  liberal  contact 
surface.  The  moving  contacts  of  each  pole  of  the  breaker  are 
connected  to  the  mechanism  by  an  insulating  rod.  The  contact 
pressure  is  obtained  by  adjustable  features  which  equalize  the 
pressure  on  both  ends  of  the  moving  contact  element. 

Arcing  Tips. — The  main  contacts  are  protected  from  burning 
when  opening  heavy  overloads  or  short  circuits  by  the  use  of  butt- 
type  arcing  tips.  The  moving  member  consists  of  a  plunger 
actuated  by  a  spring  mounted  on  the  support  of  the  moving  main 
contact  brush.  A  copper  arcing  tip  is  bolted  on  the  main  sta- 
tionary contact  in  such  a  position  that  the  head  makes  contact 
with  a  similar  tip  on  the  arcing  plunger.  These  arcing  tips  are 
easily  and  inexpensively  renewed  when  burned.  A  flexible 
copper  strap  shunt  carries  the  current  between  movable  plungers. 

The  arcing  contacts  maintain  contact  for  a  considerable  dis- 
tance after  the  main  contacts  open;  and,  being  placed  outside  the 
main  contacts,  the  arc  formed  between  them  is  automatically 
blown  away  from  the  main  contacts,  the  auxiliary  contacts  thus 
taking  all  the  arc. 

Type  E. — These  oil  circuit  breakers  were  originally  built  for 
hand  operation  only  and  designed  for  mounting  in  a  masonry 
compartment.  In  1904  they  were  listed  up  to  100  amperes  at 
25,000  volts,  300  amperes  at  16,500  volts,  600  amperes  at  7500 
and  1200  amperes  at  3500.  Their  rating  converted  to  the  modern 


OIL  CIRCUIT  BREAKERS 


135 


methods  of  figuring  would  be  expressed  in  amperes  corresponding 
to  about  65,000  K.V.A.  at  the  various  voltages  mentioned. 

Old  Forms. — The  smaller  frame  breakers  that  had  been  uti- 
lized in  the  300  and  600- ampere  sizes  for  cell  mounting  became  the 
E-l  breakers  for  cell  mounting;  the  larger  breakers  for  cell 
mounting  became  the  E-2  and  the  corresponding  frame  mounted 
breakers  became  the  E-3  and  E-4,  these  being  suitable  for  mount- 
ing against  a  flat  wall  or  on  structural  iron  framing. 

To  facilitate  erection,  dismantling  and  repairs  or  inspection, 
the  design  of  the  E-2  was  modified  so  that  each  pole  could  easily 
be  slid  into  a  steel  channel  set  in  the 
barrier  walls  between  poles.  The  result- 
ing design  with  a  soapstone  top  was 
known  as  the  E-5  and  the  pole  width 
could  be  modified  within  certain  limits 
by  changing  the  size  of  the  soapstone 
base. 

Later  Types. — When  a  definite  width 
became  standard  and  the  top  was  made 
of  steel  in  place  of  soapstone,  the  E-6 
came  into  being  and  the  same  switch 
for  frame  mounting  became  the  E-7. 

Where  a  breaker  of  the  'E'  line  was 
desired  but  a  smaller  rupturing  capacity 
than  that  of  the  E-6  would  suffice,  a 
smaller  breaker  was  developed  for  cell 
mounting  known  as  the  E-8,  and  for 
frame  mounting  known  as  the  E-9. 
For  the  neutral  circuits  of  generators 
and  for  single  phase  circuits  fed  from 
3-phase  4-wire  systems,  single-pole 
solenoid  breakers  were  developed,  known 
as  the  E-10,  an  adaptation  of  the  older  "E"  mechanism  being 
used.  Three-pole  breaker  design  has  the  three  poles  on  a  com- 
mon frame,  although  occasionally  three  independent  solenoids 
are  used. 

Fig.  85  shows  a  type  E-6  cell  mounting,  electrically  op- 
erated breaker  in  the  open  position  with  one  tank  lowered  and 
two  double  doors  of  the  cell  structure  removed. 

Fig.   86   shows  a  2000-ampere  4500-volt  E-8  breaker,  single- 


FIG.  85. — Westinghouse 
type  ' '  E  -  6  ' '  oil  circuit 
breaker,  300  amps.,  25  K.V. 


136        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


pole  unit  with  tank  removed,  showing  the  stationary  and  mov- 
ing contacts 

The  type  E  oil  circuit  breakers  are  particularly  adapted  to  the 
control  of  alternating-current  circuits  of  capacity  from  25,000  to 
40,000    connected  turbo-gen- 
erator   K.V.A.   and  voltages 
not  over    25,000.     They  are 
designed  for  indoor  mounting 
apart   from  the  switchboard 
and    for    either     manual    or 
electrical  control. 

Features. — The  following 
features  particularly  adapt 
the  type  E  breakers  to  their 
class  of  service.  Self-clean- 
ing form  of  high-pressure 
laminated  brush;  main  con- 
tacts protected  by  extra 
heavy  arcing  contacts;  sub- 
mersion and  opening  of  all 
contacts  under  oil;  quick 
opening  of  contacts,  assisted 
by  heavy  accelerating  spring; 
open  position  maintained  by 
gravity;  strong  elliptical  lap- 
welded  steel  tanks  and  steel 
tank  supports;  tanks  remov- 
able without  disturbing  the 
operating  mechanisms  or  con- 
tacts, making  inspection  easy; 
individual  tanks  enclose  the 
contacts  of  each  pole  of  the 
breaker;  ample  air  space  at 
top  of  tank  to  allow  for 
proper  gas  expansion;  in- 
sulating linings  in  tanks;  unit-type  electrical  operating  mechanism 
having  closing,  tripping,  accelerating,  and  shock-absorbing  fea- 
tures self  contained;  manually  operated  breakers  tripped  free  of 
the  mechanical  remote  control  in  the  automatic  overload-trip 
forms;  inability  to  hold  full-automatic  overload-trip  forms  of 
breaker  in  the  closed  position  when  an  excessive  overload  or 


FIQ.    86.  —  Westinghouse    type    E8   oil 
circuit  breaker. 


OIL  CIRCUIT  BREAKERS 


137 


short  circuit  exists  on  the  line;  each  pole  a  complete  unit, 
operated  by  independently  adjustable  connecting  rods  to  the 
common  electric  or  manual  operating  mechanism,  and,  in  the 
cell  mounting  forms,  installed  in  a  separate  masonry  compartment. 
Ratings. — The  following  sizes  are  built  in  either  two,  three,  or 
four- pole  breakers,  manually  or  electrically  operated. 


Interrupting 

Maximum  Amperes 

capacity 

Type 

Maximum 
volts 

in  arc 
amperes 

60  cycle 

25  cycle 

at  rated 

voltage 

E-6and  E-7.. 

300 

400 

25,000 

5,350 

E-6and  E-7.. 

600 

750 

25,000 

5,350 

E-6and  E-7.. 

1,200 

1,350 

25,000 

5,350 

E-6and  E-7.. 

1,600 

1,800 

15,000 

10,000 

E-6and  E-7.. 

2,000 

2,250 

15,000 

10,000 

E-8and  E-9.. 

600 

400 

25,000 

2,200 

E-8and  E-9.. 

600 

750 

25,000 

2,200 

E-8and  E-9.. 

1,200 

1,350 

15,000 

4,500 

E-8  and  E-9.  . 

1,600 

1,800 

7,500 

10,300 

E-8  and  E-9.  . 

2,000 

2,250 

4,500 

18,200 

Solenoid  Control. — These  breakers  are  operated  by  a  solenoid 
mechanism  that  is  mounted  above  the  poles  on  the  cell  mount- 
ing breakers  or  on  the  floor  for  the  wall,  pipe  frame  or  struc- 
tural frame  mounting  breakers.  The  breaker  is  closed  by  a 
solenoid  and  is  held  closed  by  a  hardened  steel  latch  and  a  trigger 
which  engage  automatically.  The  closing  solenoid  is  regularly 
furnished  for  use  on  125- volt  (normal)  direct- current  circuits  and 
has  a  standard  operating  range  from  70  to  140  volts.  Coils  for 
other  than  standard  voltage  with  the  same  proportionate  range 
can  be  furnished.  Due  to  the  wide  operating  range,  breakers 
with  the  standard  coil  can  be  satisfactorily  operated  from  110- 
volt  direct- current  circuits. 

Type  E-6  and  E-7  breakers  have  a  device  known  as  a  "cut- 
off" switch  supplied  as  an  integral  part  of  the  electric  operating 
mechanism.  When  properly  connected  and  adjusted,  it  does 
not  allow  an  automatic  breaker  being  held  closed  on  over  load 
thus  securing  the  trip-free  feature. 


138        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Mounting. — These  breakers  are  made  for  either  cell  or  pipe 
mounting.  The  cell  mounting  breakers,  types  E-6  and  E-8,  are 
arranged  for  supporting  the  individual  poles  of  the  breaker  in 
fire  proof  compartments  of  brick,  asbestos  lumber,  or  concrete 
structure  with  removable  doors.  The  channel  frame  upon  which 
the  manually  operated  mechanism  or  electrically  operated  mech- 
anism is  mounted  is  placed  on  top  of  the  cell  structure.  This 
construction  provides,  where  necessary,  for  special  wide  spacing  of 
the  poles  when  reactance  coils,  two  sets  of  disconnecting  switches, 
etc.,  are  used  in  connection  with  the  breaker. 

The  pipe  mounting  breakers,  types  E-7  and  E-9,  are  designed  for 
mounting  on  horizontal  pipe  supports.  All  capacities  of  both 
types  have  the  same  dimensions  of  horizontally  arranged  pipe 
centers  so  that  the  installation  of  several  different  capacities 
can  be  made  on  a  common  pipe  frame  structure. 

Unit  Construction. — The  type  E  breakers  are  made  up  of 
single-pole  units,  each  having  its  own  steel  supporting  frame  and 
toggle  arrangement  for  operating  its  moving  contacts,  so  that  all 
contact  adjustments  are  made  and  locked  before  shipment. 
In  the  multipole  breakers  these  individual  pole  mechanisms  are 
in  turn  connected  to  a  common  operating  mechanism  controlled 
by  the  manually  operated  handle  and  trip  coils  or  by  the  electric 
operating  mechanism. 

The  individual  toggle  arrangement  for  each  pole  permits  each 
complete  pole  to  be  placed  in  position  and  properly  lined  up. 
This  arrangement  also  permits  the  adjustment  of  contact  pres- 
sure and  contact  travel  of  each  pole  to  be  made  independent  of 
the  other  complete  breaker  poles. 

On  the  cell  mounting  breakers  the  operating  mechanism 
is  mounted  on  a  plate  and  channel  frame  structure  fastened  to  the 
top  of  the  cell  structure.  On  the  pipe  mounting  breakers  the 
mechanism  is  mounted  on  the  floor,  to  one  side  of  the  poles. 

Latest  Improvements. — Some  of  the  latest  improvements  in 
the  E-6  breakers  are  the  tank  cradle  and  tie  rod  method  of  sup- 
porting the  tanks  to  obviate  the  possibility  of  the  tanks  being 
blown  off  by  an  explosion  and  the  furnishing  of  reversed  brushes 
on  all  breakers  where  the  short-circuit  current  on  the  system 
might  rise  to  such  a  point  that  the  magnetic  stresses  would 
straighten  out  any  ordinary  brush  of  the  usual  wound  copper 
strip  construction.  Instead  of  the  brush  in  the  form  of  a  half 
ellipse  being  on  the  movable  member,  that  member  was  made 


OIL  CIRCUIT  BREAKERS 


139 


essentially  straight  and  brushes  in  the  form  of  a  quarter  of  an 
ellipse  were  placed  on  the  stationary  contacts  with  the  concave 
side  down  and  turned  in  so  that  the  magnetic  force  increased  the 
pressure  between  the  stationary  and  movable  members  instead 
of  tending  to  diminish  the  pressure  by  straightening  out  the 
brush  when  it  was  mounted  with  the  concave  side  downward. 
The  new  moving  element  is  so  stiff  mechanically  that  the  mag- 
netic forces  cannot  distort  its  shape. 

Type  C. — The  modern  type  C  oil  circuit-breakers  are  adapted 
to  the  control  of  circuits  of  large  capacity,  up  to  60,000,  con- 
nected turbo-generator  K.V.A.  and  up  to  15,000  volts.  They  are 
made  for  indoor  cell  mounting  and  for  electrical  operation  only. 
They  are  especially  used  for  lining  up  with  existing  installations 
of  similar  breakers,  and  are  noted  for  their  great  compactness 
with  high  rupturing  capacity. 

The  distinctive  features  of  the  type  C  breakers  are  the  self- 
contained  multipole  operating  mechanism  with  positive  and 
direct  solenoid  operation,  quick  opening  hastened  by  accel- 
erating springs  and  open  position  maintained  by  gravity.  The 
contacts  open  under  oil,  and  are  of  a  highly  efficient  form  of 
brush  with  butt  arcing  tips.  There  is  an  expansion  chamber 
with  baffled  vent  for  the  arc  gases.  The  poles  are  isolated 
in  separate  tanks  and  cells,  the  elliptical  tanks  being  very  strong, 
with  exceptionally  strong  fastenings,  and  removable  without 
disturbing  any  other  part  of  the  breaker. 

Ratings. — The  following  sizes  are  built  in  three  or  four-pole 
units  electrically  operated  with  either  vertical  or  horizontal 
arrangement  of  leads. 


Maximum 

Amperes 

Interrupting 
capacity 

Type 

60  cycle 

25  cycle 

volts 

amperes 
at  rated 
voltage 

CG  
CG 

600 
1  200 

750 
1  350 

15,000 
15,000 

14,000 
14,000 

C-2  
C-2  
C-2  

600 
1,200 
2,000 

750 
1,350 
2,250 

25,000 
25,000 
15,000 

8,000 
8,000 
15,000 

C-2  

3,000 

3,400 

2,500 

86,300 

140        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

The  breaker  is  designed  for  supporting  the  individual  poles  in 
fireproof  compartments  of  brick  or  concrete  structure  with 
removable  doors.  Each  pole  of  the  breaker  is  covered  by  a  cell 
door  consisting  of  a  metal  frame  with  asbestos  panels  and  hinged 
at  the  top  to  the  iron  mechanism  base.  The  electric  operating 
mechanism  which  controls  all  poles  simultaneously  is  mounted  on 
the  cast-iron  bedplate  or  base  which  covers  the  top  of  the  cell 
structure. 


FIG.  87. — Westinghouse  type  "C"  circuit  breaker  installation. 

Cells. — These  breakers  worked  into  very  satisfactory  structural 
arrangements,  particularly  in  plants  where  the  galleries  could  be 
so  arranged  that  one  row  of  breakers  would  be  on  a  gallery  below 
the  busbars  and  the  other  one  on  a  gallery  above  the  bus.  They 
also  were  well  fitted  for  installations  with  the  bus  bar  back  of  the 
breakers  and  particularly  for  a  feeder  and  group  arrangement, 
such  as  has  been  employed  in  many  plants,  that  permit  a  generator 
to  be  readily  used  with  either  of  two  feeder  groups  immediately 
adjacent  to  it  or  to  be  connected  to  a  main  bus  to  facilitate  paral- 
lel operations  or  tied  on  to  a  transfer  bus  to  allow  it  to  feed 
any  set  of  feeder  groups.  Fig.  87  shows  an  installation  of  'C' 


OIL  CIRCUIT  BREAKERS  141 

breakers  arranged  for  group  feeder  operation  with  one  row  of 
breakers  on  an  upper  gallery  with  the  generator  bus  back  and 
above  it,  and  a  main  bus  back  of  the  lower  part  of  the  breaker. 
On  the  floor  below,  the  feeder  breakers  are  arranged  with  the 
bus  above  them.  There  are  two  complete  sets  back  to  back 
arranged  for  a  ring  system. 

Tanks. — In  the  type  CG  breaker,  the  tank  construction  is  the 
same  as  that  for  the  type  G-l  oil  circuit  breaker,  consisting  of 
heavy  sheet  steel  tanks,  double  lap-welded  on  the  vertical 
seam,  and  having  the  bottom  flanged  outside  and  lap-welded. 

In  the  type  C-2  breaker,  the  tank  construction  is  the  same  as 
that  for  the  type  "E"  oil  circuit  breaker  except  that  the  top 
engages  a  flange  on  the  expansion  chamber  instead  of  on  the 
supporting  frame  as  in  the  "E"  breaker. 

In  the  type  CG  breaker,  the  expansion  chamber  is  supported 
from  the  3^-inch  sheet  steel  bedplate  by  strong  steel  rods. 

In  the  type  C-2  breaker,  wood  strain  insulators  support  the 
expansion  chamber  from  the  slate  base  portion  of  the  bedplate, 
thus  completely  insulating  the  tank  unit  from  ground. 

In  both  types  of  breakers,  the  expansion  chamber  provides  a 
large  space  above  the  oil  level,  into  which  the  gases  formed 
between  contacts  by  the  arc,  at  the  time  of  opening  the  circuit, 
can  expand.  Each  chamber  has  a  vent  to  provide  an  exit  for 
gases  and  these  vents  are  baffled  to  prevent  the  throwing  of  oil 
when  the  breaker  opens  under  heavy  overloads  or  short  circuits. 

Mechanism. — The  mechanism  with  operating  coils  is  self 
contained  on  a  single  bedplate  or  base.  To  make  the  opening  of 
the  breaker  rapid  and  positive,  accelerating  springs  are  used  to 
force  the  breaker  to  the  open  position.  Dashpots  absorb  the 
momentum  of  the  mechanism  in  closing  and  in  opening.  The 
bedplate  is  also  fitted  with  leather  bumpers  to  support  the  weight 
of  the  moving  contacts  and  rods  after  the  dashpots  have  brought 
the  breaker  to  rest  in  the  open  position. 

Type  O. — The  modifications  necessary  for  a  60-cycle  breaker 
of  about  4000-amperes  capacity,  involved  the  use  of  two 
sets  of  studs  in  parallel  or  a  total  of  four  studs  per  pole  and  this 
logically  lead  to  a  circular  design  of  tank  as  special  round  tank  E 
breakers  and  these  worked  out  so  well  that  a  modified  type  of 
mechanism  was  developed  and  a  line  of  breakers  with  16-inch 
diameter  round  tanks  became  the  type  O-l,  while  corresponding 
breakers  with  20-inch  tanks  became  the  type  O-2. 


142        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

With  the  type  O-l  or  O-2  breaker,  as  well  as  with  the 
E-6,  the  unit  type  of  construction  is  used  and  the  pole  units 
can  be  assembled  as  2,  3  or  4-pole  units  with  a  single  mechanism 
for  operating  all  the  poles  simultaneously.  Each  pole  is  nor- 
mally arranged  to  slide  into  a  channel  iron  recess  in  the  barriers 
between  adjacent  poles  and  the  two  channels  set  back  to  back 


FIG.  88. — Westinghouse  type  "O-l"  oil  circuit  breaker. 


occupy  the  same  thickness  as  a  4-inch  barrier  wall.  This  results 
in  the  minimum  spacing  between  poles  for  normal  construction. 
The  substitution  of  an  "I"  beam  for  a  double  channel  results  in 
the  saving  of  a  centre  distance  of  an  inch,  while  the  locating  of  the 
channels  outside  of  the  barrier  walls  means  slightly  greater 
spacing. 

A  typical  3-pole  breaker  type  O-l  is  shown  in  Fig.  88,  this 
being  the  type  of  the  breakers  at  the  West  Farms  substation 
of  the  New  York  Edison  Company  controlling  the  supply  of 
the  single-phase  electrification  of  the  N.  Y.  N.  H.  &  H.  R.  R. 


OIL  CIRCUIT  BREAKERS 


143 


Co.  at  that  point.     Fig.  89  is  a  3000-ampere  3-pole  type  O-2 
breaker. 


FIG.  89. — Westinghouse  type  "O-2"  oil  circuit  breaker. 

Cells. — As  the  general  type  or  cell  construction  for  the  E-6, 
O-l,  0-2  breakers  is  identical,  these  three  types  or  any  two  of 
them  can  be  readily  assembled  side  by  side  in  a  symmetrical 
structure.  When  it  is  considered  possible  that  future  growth 
in  a  station  may  require  larger  breakers  it  is  possible  to  put 
up  structures  for  the  0-2  breakers  and  slightly  modify  a  type 
O-l  or  E-6  breaker  so  that  it  can  be  arranged  readily  in  the 
larger  structure.  O-l  breakers  are  installed  in  0-2  structures 
in  the  plant  of  the  Buffalo  General  Electric  Company,  auxiliary 
channel  irons  being  utilized  to  take  up  the  difference  in  width 
between  the  two  sizes. 

The  type  O  oil  circuit  breakers  are  particularly  adapted  to  the 
control  of  systems  of  large  capacity  from  40,000  up  to  100,000 
turbo-generator  K.V.A.  where  voltages  do  not  exceed  25, 000  volts. 

This  line  supplements  the  type  E  line  of  cell  mounting  breakers, 
providing  higher  current  and  interrupting  capacities.  These 


144        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


breakers  are  supplied  in  single-pole  unit  form  for  cell  mounting 
only,  each  pole  being  mounted  in  a  separate  masonry  compart- 
ment. The  operating  mechanism  is  mounted  on  the  top  of 
the  cell  structure  on  a  channel  and  plate  base,  and  operates  the 
several  poles  as  a  single  unit. 

Tanks. — The  tanks  are  cylindrical  in  form,  seamless,  and 
with  rounded  base,  being  die  pressed  from  heavy  sheet  steel. 
They  represent  the  strongest  form  of  tank  construction  possible. 
Type  O-l  tanks  are  16  inches  in  diameter,  and  type  O-2  tanks 
20  inches  in  diameter.  These  breakers  are  built  in  the  following 
sizes,  all  cell  mounting,  electrically  operated  only,  in  2-,  3-,  or  4- 
pole  forms. 

RATINGS 


Maximum 

Amperes 

Interrupting 
Capacity 

Type 

60  cycle 

25  cycle 

Maximum 
voltage 

in  arc 
amperes 
at  rated 
voltage 

O-l  

600 

750 

25,000 

9,600 

O-l 

1  200 

1  400 

25  000 

9  600 

O-l  
O-2  
O-2  
O-2  

1,600 
2,000 
3,000 
4,000 

1,800 
2,400 
4,000 
5,000 

15,000 
25,000 
15,000 
15,000 

18,000 
12,300 
23,000 
23,000 

These  breakers  are  electrically  operated  by  the  solenoid 
mechanism  mounted  on  the  cell  top.  The  breaker  is  closed  by  a 
solenoid  and  is  held  closed  by  a  hardened  steel  latch  and  a  trigger 
which  engage  automatically.  The  closing  solenoid  is  regularly 
furnished  for  use  on  125-volt  (normal)  direct-current  circuits 
and  has  a  standard  operating  range  from  70  volts  to  140  volts. 
Coils  for  other  than  standard  voltage  with  the  same  proportion- 
ate operating  range  can  be  supplied  on  special  order.  Due  to 
the  wide  operating  range,  breakers  with  the  standard  coil  can 
be  satisfactorily  operated  from  110- volt  direct- current  circuits. 

Acceleration. — In  all  the  type  O  breakers,  an  .  accelerating 
spring  is  provided  as  part  of  the  complete  breaker  mechanism  to 
assist  in  forcing  the  breaker  to  the  open  position;  an  air  cylinder 
dashpot  in  the  lower  portion  of  the  spring  container  takes  up  the 


OIL  CIRCUIT  BREAKERS  145 

shock  of  the  moving  parts.  The  action  of  this  dashpot  can  be 
adjusted  by  a  screw  needle- valve  which  regulates  the  size  of 
opening  of  the  dashpot  valve. 

The  high  interrupting  capacity  rating  of  these  breakers  is 
due  to  the  form  of  tank,  the  use  of  steel  supporting  flanges  with 
steel  bolts,  steel  tops,  large  volume  and  head  of  oil,  liberally 
designed  arcing  tips  and  the  rapid  acceleration  of  the  moving 
contacts  when  opening. 

Oil  gauges  of  the  sight-glass  form  are  supplied  on  each  tank  so 
that  proper  maintenance  of  the  oil  level  is  assured  with  reason- 
able degree  of  inspection.  Drain  valves  are  supplied  on  all 
forms  of  this  breaker  so  that  when  desired,  the  tanks  can  be 
emptied  before  lowering. 

Tanks. — The  tanks  are  deep,  providing  ample  space  above  the 
oil  level  as  an  expansion  chamber  for  the  arc  gases  and  to  reduce 
slopping  of  the  oil  from  internal  disturbances.  The  gases  are 
vented  through  specially  designed  check-valves,  providing  full 
venting  of  gases,  but  at  the  same  time  preventing  passage  of  oil. 

Arcing  contacts  of  the  spring-actuated,  butt  type  protect  the 
main  current-carrying  contacts.  Each  part  can  be  easily  re- 
placed at  little  expense.  The  arcing  contacts  open  only  after  the 
main  contacts  have  separated  a  considerable  distance.  As  they 
are  placed  outside  the  main  contacts  so  that  the  magnetic  blow  out 
effect  of  the  current  will  blow  the  arc  away  from  them,  the 
main  contacts  are  fully  protected  from  any  possibility  of  arcing. 

A  modification  of  the  design  permits  these  breakers  to  be 
made  for  frame  mounting  and  the  mechanism  can  be  placed  on 
the  floor  at  one  side  or  in  any  of  several  different  locations  to 
suit  the  desired  arrangement  of  the  station. 

Specially  wide  spacing  has  been  used  in  a  few  particular  cases 
where  breakers  were  used  with  bus  reactors  and  the  pole  spacing 
was  to  match  that  of  the  reactors. 

Type  CO. — Where  great  compactness  and  high  rupturing 
capacity  is  desired  the  CO  line  can  be  used,  these  being  essentially 
O-l  or  O-2  poles  with  a  simple  compact  mechanism  something 
like  that  of  the  type  C. 

The  type  CO  oil  circuit  breakers  in  general  perform  on  circuits 
of  not  over  15,000  volts,  the  same  service  as  the  type  O  line, 
but  in  more  compact  space.  They  have  a  unit-type  electric 
operating  mechanism,  forming  part  of  an  entirely  self  containing 
breaker  as  shown  in  Fig.  90  which  requires  no  intermediate 
10 


146        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

walls  in  the  cell  structure  for  supporting  individual  poles.  The 
complete  breaker  is  shipped  in  one  piece,  except  for  the  doors  and 
barriers,  with  all  adjustments  of  contacts  and  mechanical  parts 
locked,  thus  reducing  the  installation  work. 


Comportments  ifllo-ftrtt  0* 


FIG.  90. — Westinghouse  oil  circuit  breaker  type  COl. 

Ratings. — The  following  sizes  are  built  only  in  3-pole  elec- 
trically operated  cell  mounting  form. 


Maximum  Amperes 


TVnp 

Capacity 

iype 

60  cycles 

25  cycles 

volts 

amperes 
at  rated 
voltage 

CO-1  
CO-1 

600 
1  200 

800 
1  500 

15,000 
15  000 

18,000 
18  000 

CO-1  

1,600 

2,000 

15,000 

18,000 

CO-1 

2,000 

2,400 

15  000 

18  000 

CO-2  
CO-2  
CO-2 

600 
1,200 
1  600 

800 
1,600 
2  000 

15,000 
15,000 
15  000 

23,000 
23,000 
23  000 

CO-2  
CO-2  

2,000 
2,400 

2,400 
3,000 

15,000 
15,000 

23,000 
23,000 

Interrupting 


OIL  CIRCUIT  BREAKERS  147 

The  type  CO  breakers  are  made  for  mounting  in  brick,  concrete, 
or  steel  structure  compartments.  The  two  outstanding  features 
of  the  type  CO  breaker  are  its  compactness  and  its  ease  of 
installation.  No  intermediate  structure  walls  are  required 
for  supporting  the  individual  poles,  all  of  them  being  supported 
from  the  common  steel  top.  The  breaker  is  supported  in  the 
structure  compartment  by  means  of  anchor  plates  set  in  and 
projecting  from  the  cell  walls.  The  steel  top  of  the  circuit 
breaker  rests  on  these  anchor  plates  and  bolts  hold  it  securely  in 
place.  The  space  between  the  circuit-breaker  top  and  the  floor 
in  front  of  the  circuit-breaker  tanks  is  covered  with  removable 
doors.  Three  doors  are  furnished  with  each  standard  3-pole 
breaker.  Each  door  consists  of  a  metal  frame  with  asbestos 
panels  and  is  hinged  at  the  top  to  the  mechanism  base. 

Type  G. — The  type  G  oil  circuit  breakers  of  modern  design 
comprise  a  complete  line  of  high  voltage  breakers  for  indoor  or 
outdoor  use.  Four  forms  of  these  breakers  are  built,  known  as 
types  'GA,'  'G-l,'  'G-2'  and  'G-ll.'  Each  form  has  a  different 
interrupting  capacity  with  corresponding  differences  in  con- 
struction. 

The  type  G  breakers  all  have  the  condenser  type  of  terminal 
bushings,  steel  tanks  with  welded  seams,  and  large  expansion 
chamber  with  baffled  vents  for  the  arc  gases. 

All  type  G  breakers  can  be  had  in  automatic  or  non-automatic 
forms.  Automatic  overload  tripping  can  be  obtained  either 
from  separate  current  transformers  or  from  bushing  type  current 
transformers  which  are  slipped  over  the  breaker  terminal  bush- 
ings. 

Sizes. — These  breakers  are  available  for  all  voltages  from 
22,000  to  155,000  indoor  or  outdoor,  manual  or  electrically  oper- 
ated. They  are  available  for  frame  mounting  up  to  and  including 
73,000  volts.  With  interrupting  capacities  of  from  1440  to  5350 
arc  amperes  per  phase  at  rated  voltage  available  with  different 
types,  the  requirements  of  present  high  voltage  systems  are  well 
met  with  this  line  of  breakers.  Practically  all  such  breakers 
are  arranged  for  solenoid  operation  as  3-pole  units  and  are 
built  with  a  separate  steel  tank  for  each  pole  of  each  breaker. 
Usually  these  steel  tanks  are  so  arranged  that  their  spacing 
may  be  made  to  suit  the  wiring  of  the  installation  in  case  the 
minimum  spacing  normally  used  with  the  breakers  would  intro- 
duce undesirable  bends  in  the  wiring. 


148        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


FIG.  91. — Westinghouse  37-K.V.  oil  circuit  breaker  type  Gil. 


FIG.  92. — Westinghouse  154-K.V.  oil  circuit  breaker  type  GA. 


OIL  CIRCUIT  BREAKERS 


149 


Indoor-outdoor. — All  of  the  high  tension  breakers  can  be 
made  suitable  for  either  indoor  or  outdoor  service  but  are  usually 
supplied  for  outdoor,  so  most  of  the  illustrations  and  descriptions 
will  apply  to  the  outdoor  type  of  equipment,  but  enough  indoor 
apparatus  will  be  illustrated  to  show  the  essential  differences 
between  the  two  types. 

Up  to  73  K. V.  the  high  tension  oil  circuit  breakers  whether  for 
indoor  or  outdoor  service  are  usually  made  frame  mounting  to 
permit  the  tanks  to  be  easily  dropped  to  secure  rapid  inspection 
and  adjustment  of  the  contacts. 

Indoor. — Fig.  91  shows  a  37-K.V.  G-ll  breaker  for  indoor 
service  and  clearly  illustrates  the  pipe  framework  used  for 
supporting  the  breaker  at  such  a  height  that  the  tanks  can  be 
readily  dropped.  The  highest  voltage  breaker  that  has  been 
built  for  indoor  service  is  shown  in  Fig.  92  which  illustrates 
the  154-K.V.  type  GA  floor  mounted  breaker  furnished  to  the 
Big  Creek  Power  Company  a  number  of  years  ago. 


FIG.  93. — Westinghouse  type  GA  oil  circuit  breaker — contact  details. 

Quick  Break. — Circuit  breakers  for  high  voltage  service  such  as 
these  illustrated  involve  long  travel  of  the  contacts  and  heavy 
moving  elements  and  therefore  are  arranged  to  embody  a  special 
quick  break  feature  for  the  rapid  separation  of  the  arcing  contact 
which  is  so  essential  on  a  high  power  interrupting  service. 

Fig.  93  shows  the  contact  details  employed  with  the  154 


150        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

K.V.  breaker.  The  lower  end  of  the  condenser  terminal  bushing 
is  enclosed  in  a  porcelain  arc  shield  for  protection  from  the  arcs 
that  arise  during  operation.  Between  this  arc  shield  and  the 
stationary  contact  is  a  metallic  static  shield  for  distributing 
the  stress  uniformly  over  the  surface  of  the  terminal  bushings. 
The  main  contacts  are  of  the  butt  type,  each  terminal  having 
two  main  contacts  and  two  arcing  contacts,  the  latter  being 
designed  to  take  all  of  the  arcing  so  that  the  main  contact  will 
not  become  pitted  or  burned  by  the  arc.  The  entire  stationary 
contact  is  enclosed  in  a  metal  hood  which  distributes  the  electro- 
static stress  that  might  otherwise  be  excessive  due  to  the  sharp 
corners  on  the  edges  of  the  contact  mechanism. 

Arcing  Contact. — The  arcing  contacts  attached  to  the  sta- 
tionary terminals  of  the  breaker  are  so  arranged  that  in  the 
closed  position  they  are  latched  in  touch  with  the  corresponding 
arcing  contacts  on  the  movable  member.  When  the  breaker 
opens  the  main  contacts  separate  at  once,  but  the  latch  holds  the 
arcing  contacts  together,  forcing  the  upper  one  to  be  pulled 
down  against  the  compression  of  a  spring  for  a  distance  of  ap- 
proximately 7  inches.  After  the  moving  member  has  dropped 
the  7  inches,  the  latch  releases  and  the  spring  retrieves  the  upper 
arcing  contact,  breaking  the  circuit  very  quickly. 

The  break  in  the  circuit  occurs  in  the  free  oil  and  the  natural 
tendency  of  the  gas  bubble  to  rise  is  not  in  any  way  impeded. 
The  magnetic  effect  of  the  current  passing  down  one  stationary 
contact  across  the  moving  member,  and  back  the  other  stationary 
contacts  is  such  as  to  blow  the  oil  away  from  the  contact  and 
toward  the  side  of  the  case.  This  effect  together  with  the  natural 
tendency  of  the  gas  bubble  to  rise  through  the  oil  enables  the  arc 
to  be  quickly  carried  away. 

While  the  descriptions  that  follow  apply  to  outdoor  breakers, 
corresponding  indoor  breakers  differ  only  from  the  outdoor  ones 
in  the  omission  of  the  rain  shields  from  the  condenser  bushing 
terminals  and  certain  minor  changes  in  the  housing  of  the  mech- 
anism and  the  venting  of  the  tanks. 

37  K.V. — Fig.  94  shows  a  400-ampere  37-K.V.  3-pole  solenoid 
operated  frame  mounted  outdoor  breaker  with  one  tank  removed 
to  show  the  contacts.  This  breaker  has  a  guaranteed  rupturing 
capacity  of  1700  amperes  at  37  K.V.  With  the  frame  mounting 
it  is  possible  to  drop  the  tank  on  any  one  pole  to  obtain  ready 
access  to  the  contacts. 


OIL  CIRCUIT  BREAKERS 


151 


FIG.  94. — Westinghouse  type  "G-ll"  outdoor  oil  circuit  breaker,  400  amps. 
37  K.V. 


FIG.  95. — Westinghouse  type  "G-ll"  outdoor  oil  circuit  breaker,  400  amps., 
73  K.V. 


152        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

73  K.V.— Fig.  95  shows  a  400-ampere  73-K.V.  solenoid  op- 
erated outdoor  frame  mounting  oil  circuit  breaker  having  a 
guaranteed  rupturing  capacity  of  2400  amperes  at  73  K.V. 
This  breaker  has  elliptically  shaped  oil  tanks  made  of. steel  plate 
with  lap-welded  seams  and  a  cast  steel  top  of  domed  shape  to 
secure  ample  strength  against  explosion.  The  tanks  are  ar- 
ranged for  suspension  from  the  supporting  frame  and  are  hung 
by  suitable  tie  bolts  connected  to  a  supporting  grid  beneath 
the  tank.  An  overhung  lip  around  the  top  is  interlocked  with 
the  tank  rim  and  suitable  packing  between  the  top  and  the  rim 
insures  waterproof  joints.  A  suitable  removable  cover  with 
interlocking  rim  gives  access  to  the  upper  portion  of  circuit- 
breaker  mechanism.  Conduit  pipe  with  packing  washers  and 
lock  nuts  affords  weatherproof  communication  from  pole  to  pole 
for  the  operating  levers  and  for  the  control  leads  when  required. 
Solenoid  operated  mechanism  is  located  at  one  end  of  the  unit, 
housed  in  a  case  or  box  with  a  removable  cover  having  packed 
joints.  This  box  has  conduit  pipe  for  connection  to  the  circuit- 
breaker  mechanism. 

The  steel  top  in  addition  to  supporting  and  protecting  the 
operating  mechanism  is  arranged  to  form  an  expansion  chamber 
to  cushion  the  pressure  caused  at  the  instant  of  interrupting  the 
circuit.  As  considerable  oil  vapor  and  gas  may  collect  in  this 
chamber,  suitable  baffled  vents  are  placed  in  such  positions  as  to 
relieve  sudden  air  pressures,  and  in  addition,  to  induce  circulation 
of  air  through  the  chamber  to  drain  out  the  accumulating  oil 
vapor.  As  the  oil  is  of  more  or  less  volatile  nature,  this  latter 
function  is  of  considerable  importance.  To  prevent  the  trans- 
mission of  a  disturbance  in  one  tank  to  adjacent  tanks  and  to  the 
box  containing  the  operating  mechanism  and  solenoid,  suitable 
baffles  can  be  placed  in  the  connecting  conduit  pipe.  Pressure 
can  be  vented  to  the  outside,  but  propagation  of  pressure  from 
tank  to  tank  will  be  prevented. 

The  terminal  bushings  are  sufficiently  protected  by  petti- 
coated  insulators  to  afford  insulation  under  the  most  severe 
conditions  of  driving  rain,  wet  snow  or  sleet.  It  is  not  uncom- 
mon to  find  the  entire  structure,  including  the  exposed  portions 
of  the  porcelain  insulators,  incased  in  a  coating  of  sleet,  or  to 
see  snow  piled  up  practically  to  the  entire  height  of  the  terminal 
bushings. 


OIL  CIRCUIT  BREAKERS 


153 


Frame  Mounting. — On  circuit  breakers  of  small  and  moderate 
size  where  the  weight  of  the  oil  tanks  and  oil  is  not  prohibitive, 
the  frame  mounting  arrangement  of  circuit  breaker  is  highly 
desirable  as  it  permits  the  ready  removal  of  the  oil  tanks  for  the 
purpose  of  inspecting  the  contact  details  and  the  operating 
mechanism  without  disturbing  the  line  connections. 

Platform  Mounting. — Breakers  for  higher  voltages  and  larger 
rupturing  capacities  are  usually  made  platform  mounting  owing 
to  the  difficulty  of  lowering  the  tank  filled  with  oil. 


FIG.  96. — Westinghouse  type  "G-ll"  outdoor  oil  circuit  breaker,  400  amps., 
95  K.V. 

With  the  larger  breakers  access  to  the  interior  of  the  tanks  is 
secured  by  the  removal  of  the  mechanism  cap  which  exposes  the 
lever  system  and  presents  a  sufficiently  large  opening  to  withdraw 
any  necessary  part.  The  mechanism  is  ordinarily  so  arranged 
that  a  terminal  bushing  complete  with  its  contact  details  can  be 
withdrawn  without  disturbing  any  other  details,  and  the  moving 
contact  elements  can  also  be  withdrawn  through  the  manhole 
or  mechanism  cover. 

Experience  has  indicated  the  desirability  of  providing  a  struc- 
tural frame  or  platform  that  will  permit  access  to  the  bottom  of 


154        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

the  tank,  allowing  free  air  circulation  as  this  assists  in  keeping  all 
parts  free  from  rust  and  corrosion. 

In  certain  cases  the  tank  bases  are  made  with  openings  in  the 
rim  so  that  the  bottom  of  the  tanks  can  be  painted  with  a  long- 
handled  brush  if  the  foundation  is  of  concrete  or  masonry  that 
would  otherwise  make  it  difficult  to  get  at  the  bottom  of  the 
tanks. 

Platform  Type. — A  typical  outdoor  platform  mounted  breaker 
is  shown  in  Fig.  96  which  illustrates  a  95-K.V.  400-ampere 
breaker  with  elliptical  tanks  having  a  guaranteed  rupturing 
capacity  of  2400  amperes  at  95  K.V. 


FIG.  97. — Westinghouse  type  "G-2"   outdoor  oil  circuit  breaker,  400  amps., 
135  K.V. 

Type  G-2. — The  type  G-2  oil  breaker  is  of  "all-steel  construc- 
tion" and  has  a  tank  of  the  strongest  possible  construction. 
The  shape  of  the  tank  is  cylindrical  with  spheroidal  top  and 
bottom,  having  the  same  radius  of  curvature  as  the  sides.  This 
form  of  tank  having  all  seams  riveted  is  tested  to  withstand  a 


OIL  CIRCUIT  BREAKERS 


155 


static  pressure  of  150  pounds  per  square  inch.  The  steel  top 
and  bottom  are  flanged  inside  and  riveted  to  the  tank  body, 
completing  a  form  of  construction,  all  details  of  which  are  directly 
comparable  to  that  followed  in  the  best  high-pressure  boiler 
practice. 


FIG.  98. — Westinghouse  type   "GA"   outdoor  oil  circuit  breaker,   400  amps., 
135  K.V. 

This  construction  takes  full  cognizance  of  gas  pressures  which 
accompany  the  interruption  of  high  voltage  large  ampere  capa- 
city arcs.  Of  necessity  these  pressures  are  transmitted  equally 
through  the  surrounding  oil  medium  to  the  walls  of  the  containing 
vessel.  Due  to  the  voltage  and  power  of  the  arc,  reliance  is 
placed  on  a  large  head  of  oil  aiding  the  natural  buoyancy  of  gas 
bubbles  to  present  an  ever  changing  mass  of  cool  and  clean  oil 
to  the  arc  while  at  the  same  time  the  mechanical  strength  of  the 


156        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

containing  vessel  is  made  ample  to  withstand  pressures  that  may 
be  transmitted  from  the  arc  through  the  oil  medium.  Past 
operating  experience  with  high  powered  moderate  voltage  systems 
has  shown  the  danger  involved  in  trying  to  confine  this  arc  to 
too  small  a  vessel  with  a  low  head  and  small  volume  of  oil. 
This  is  particularly  true  when  recognition  is  given  to  the  demands 
of  modern  operation  for  a  breaker  to  be  capable  of  opening  its 
rated  interrupting  capacity  in  arc  amperes  twice  within  an 
interval  of  two  minutes. 

The  large  size  of  these  circular  tanks  with  the  consequent 
immense  volume  of  oil,  strength  of  materials  and  construction, 
depth  of  contacts  below  the  oil  level  and  the  rapidity  with  which 
the  contacts  are  opened,  result  in  a  breaker  entirely  adequate  for 
the  largest  power  systems. 

Fig.  97  shows  a  400-ampere,  135-K.V.,  3-  pole  breaker 
having  a  guaranteed  rupturing  capacity  of  4300  amperes  per 
phase  at  135  K.V.  This  breaker  was  furnished  to  the  West 
Penn  Power  Company  for  132-K.V.  service  and  a  modification  of 
it  is  available  for  155-K.V.  service 

Type  GA.— Fig.  98  shows  the  400-ampere  135-K.V.  electric- 
ally operated  oil  circuit  breaker  having  a  guaranteed  rupturing 
capacity  of  1600  amperes  at  135  K.V.  A  number  of  these  breakers 
are  in  service  in  Michigan. 

Designs  have  been  prepared  for  breakers  for  use  on  220-K.V. 
circuits,  and  some  are  now  being  built. 


CHAPTER  V 
RELAYS 

Functions. — Modern  distributing  systems  require  protection 
more  selective  and  flexible  than  that  afforded  by  the  usual  control 
features  of  automatic  circuit  breakers  and  this  need  is  supplied 
by  automatic  devices  known  as  relays  which  trip  a  circuit  breaker 
upon  the  occurrence  of  some  predetermined  change. 

Types. — Relays  are  built  to  furnish  protection  on  A.C.  or  D.C. 
circuits  against  overvoltage,  no  voltage,  overload,  no  load,  reverse 
load  and  reverse  phase  and  such  relays  either  directly  or  in  con- 
nection with  other  relays  may  be  made  instantaneous  or  provided 
with  a  time  limit  either  of  definite  duration  or  inversely  propor- 
tional to  the  extent  of  overload,  etc. 

Definite  Time. — This  type  is  used  with  circuits  where  the 
service  must  be  maintained  at  all  hazards  no  matter  how  great 
is  the  overload  provided  it  does  not  last  more  than  a  definite 
period  of  time  say  from  2  to  4  seconds,  depending  on  the  ability 
of  the  system  to  withstand  such  conditions  and  the  length  of  time 
required  for  various  feeder  breakers  to  trip  out,  relieving  the 
system  protected  by  the  breaker  with  definite  time  limit. 

Inverse  Time. — This  relay  gives  a  selective  action  varying 
inversely  with  the  load  so  that  usually  the  faulty  line  carrying  the 
heavier  load  will  have  its  breaker  tripped  out  before  the  other 
breakers  are  affected. 

D.C.  RELAYS 

Overload. — The  D.C.  overload  relays  of  the  Condit  Electrical 
Manufacturing  Company  are  made  with  series  coils  in  the  form 
of  a  solenoid  for  current  ratings  from  5-600  amperes  as  shown 
in  Fig.  99.  For  currents  from  800-3000  amperes  the  magnetic 
circuit  is  arranged  to  slip  over  a  round  stud  while  for  currents  from 
800-8000  amperes  the  magnetic  circuit  can  be  put  around  the 
copper  strap  connections  in  the  leads  or  bus.  These  relays 
are  made  as  instantaneous  or  with  inverse  time  limit  features. 

157 


158        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

A  modification  of  the  arrangement  is  made  by  the  addition  of 
the  voltage  coil  that  changes  the  relay  to  a  D.C.  reverse  power 
relay  with  the  current  element  to  slip  over  a  circular  stud. 


FIG.  99. — Condit  Electric  &  Mfg.  Co.  type  "DC"  relay. 

Reverse. — When  an  adjustable  reverse-current  D.C.  relay 
with  time  limit  is  desired,  a  type  of  relay  is  used  built  on  the 
principle  of  a  permanent  magnet  D.C.  ammeter  operated  from 
a  shunt.  In  normal  operation  the  armature  of  the  relay  tends  to 
turn  in  one  direction  but  is  restrained  by  a  stop,  while  in  the  case 
of  reversal  the  armature  turns  in  the  opposite  direction,  its 
movement  being  restrained  by  a  spring  and  being  proportional 
to  the  strength  of  the  current  in  the  reverse  direction. 
The  angle  through  which  the  armature  has  to  turn  to  close  the 
contacts  is  adjustable  by  moving  the  stationary  contact.  The 
inverse  time  element  feature  is  obtained  by  the  movement  of  the 
aluminum  frame,  on  which  the  armature  is  wound,  in  the  intense 
magnetic  field,  the  eddy  currents  in  the  frame  furnishing  the 


RELAYS  159 

damping  action.     A  modification  of  this  design  is  used  for  D.C. 
overload  relay. 

A.C.  RELAYS 

Overload. — One  of  the  simplest  overload  A.C.  relays  designed 
for  instantaneous  operation,  definite  time  limit  and  inverse  time 
limit,  consists  essentially  of  a  solenoid  and  core.  In  the  in- 
stantaneous relay  the  core  lifts  immediately  and  closes  or  opens 
contacts  that  trip  the  circuit  breaker  when  the  current  in  the 
coil  reaches  a  certain  value.  With  the  inverse  time  limit  the 
movement  of  the  core  is  opposed  by  a  bellows  with  an  adjustable 
valve  mounted  above  the  coil.  With  the  definite  time  limit  the 
same  kind  of  bellows  and  valve  is  used  but  the  solenoid  does  not 
work  directly  on  the  bellows.  When  the  overload  occurs  the 
core  rises  instantly  compressing  a  spring  which  in  turn  acts  on 
the  bellows.  If  the  core,  due  to  continued  overload,  keeps  the 
spring  in  compression  the  required  time,  the  air  will  be  forced 
out  of  the  bellows  and  the  tripping  circuit  operated.  This  type 
of  relay  can  be  set  for  any  time  limit  between  1  and  10  sec- 
onds. Relays  of  this  type  are  usually  operated  from  current 
transformers  but  are  sometimes  mounted  on  a  high  tension 
insulator  and  connected  in  the  high  voltage  circuit.  This  plunger 
type  of  overload  relay  has  been  practically  superseded  by  the 
induction  type. 

Radial  System. — The  proper  relaying  equipment  for  use  on 
any  A.C.  line  will  depend  among  other  things  on  the  type  of 
distribution  used.  Where  there  is  a  single  source  of  power  with 
feeders  radiating  out  from  the  generating  station  and  possibly 
passing  through  one  or  more  sectionalizing  or  transforming  sta- 
tions, proper  selective  action  can  usually  be  obtained  by  making 
the  breakers  farthest  from  the  power  house  practically  instantar 
neous  in  their  operation,  those  at  the  power  house  being  provided 
with  relays  set  for  a  definite  time  of  from  one  to  two  seconds  and 
the  intermediate  sections  being  provided  with  relays  having 
various  time  settings. 

Current  Settings. — In  addition  to  securing  discrimination  on 
the  part  of  the  relays  by  means  of  a  definite  time  feature,  it  is  also 
possible  to  discriminate  by  the  current  setting  because  trouble 
which  occurs  at  the  far  end  of  a  branch  line  will  not  draw  as 
heavy  a  current  as  though  it  were  closer  to  the  source  of  power. 
Selective  action  can  frequently  be  obtained  to  advantage  by  the 
use  of  an  inverse  time  limit  relay  having  characteristic  curves 


160        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


similar  to  those  shown  in  Fig.  100.  This  type  of  relay  has  an 
adjustable  definite  time  element  in  addition  to  the  inverse  time, 
and  the  combination  of  these  two  is  well  adapted  for  the  protec- 


800  1000  1200          1400 

Percent  Current  Required  to  Close  Contact! 

FIG.  100. — Relay  characteristic  curves. 

tion  of  circuits  of  this  kind,  because  either  the  inverse  time  part 

of  the  curve  or  the  definite  time  part  can  be  utilized,  dependant 

upon  the  particular  circuit  standard. 

Type  CO. — Such  a  combination  of  definite  time  and  inverse 

time  is  obtained  in  the  type  'CO'  Westinghouse  relay  shown  in 
Fig.  101.  This  relay  is  built  on 
the  induction  principle,  and  its 
great  success  has  been  largely  due 
to  its  remarkable  accuracy  and 
permanence  of  its  calibration.  The 
use  of  a  permanent  magnet  as  a 
time  limit  device,  prevents  over 
swinging  and  chattering  of  the  con- 
tacts, and  the  construction  is  such 
that  the  relay  will  instantly  cease 
FIG.  loi.-westinghouse  type  its  movement  when  the  over  load 

CO  definite  minimum  inverse  time     disappears. 

limit  overload  relay.  Torque    Compensator.— One    of 

the  essential  features  of  this  relay  is  the  torque  compensator 
embodied  in  its  design.  This  is  essentially  a  small  current 
transformer  having  comparatively  little  iron  in  its  magnetic 
circuit  so  that  it  saturates  at  a  little  more  than  5  amperes  in 
the  primary.  With  this  device  the  primary  current  can  be 


RELAYS  161 

momentarily  increased  to  200  times  normal  without  increasing 
the  secondary  current  more  than  a  small  percentage.  As 
it  is  this  secondary  current  that  actually  works  on  the  relay 
mechanism  the  force  of  the  relay  is  practically  constant, 
independent  of  the  amount  of  the  current,  so  that  its  speed  of 
operation  is  independent  of  the  value  of  the  short  circuit  and 
is  determined  by  the  restraining  influence  of  the  permanent 
magnet  and  the  distance  through  which  the  contact  has  to  move. 
As  this  distance  is  adjustable,  the  definite  time  setting  on  the 
standard  relay  can  be  made  anything  from  0.1  of  a  second  up  to 
2  seconds,  and  in  special  cases  up  to  4  seconds.  A  current  ad- 
justment is  also  provided  on  the  relay  so  as  to  secure  normal 
operation  with  relay  current  varying  from  4  to  12  amperes. 

Parallel  System. — Where  the  distributing  system  instead  of 
being  a  radial  one  is  provided  with  parallel  circuits  between  the 
generating  stations  and  the  points  of  distribution,  such  systems 
can  sometimes  be  protected  satisfactorily  by  means  of  inverse 
time  element  relays  if  the  short  circuit  conditions  are  such  that 
relays  of  this  type  can  properly  discriminate,  but  the  more  usual 
method  of  protecting  service  against  trouble  on  parallel  feeders 
is  to  place  reverse  power  relays  at  the  substation  end  of  each 
feeder  and  definite  time  limit  relays  at  the  generator  end. 


o 


FIG.   102.  —  Ring  arrangement  of  circuits. 

Ring  System.  —  A  modification  of  the  parallel  feeder  arrange- 
ment is  the  ring  system  where  each  substation  is  fed  from  two 
directions,  as  indicated  in  Fig.  102.  On  such  a  system  definite 
time  limit  reverse  power  relays  must  be  utilized  and  the  time 
setting  of  each  successive  relay  should  be  increased  by  a 
sufficient  amount  to  allow  time  for  the  circuit  breaker  in  the 
preceding  substation  to  open.  On  the  diagram  the  time  settings 


162        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

of  the  various  relays  have  been  marked  and  for  )£ -second  time 
interval  will  work  satisfactorily  if  the  relays  are  accurate  and  the 
circuit  breakers  quick  acting.  Such  a  system  becomes  somewhat 
more  complicated  if  power  is  fed  in  at  more  than  one  point,  as 
for  example  if  a  generator  ties  in  at  station  D.  The  adjustment 
of  the  relays  on  such  a  system  would  have  to  be  modified  depend- 
ing on  whether  the  power  was  being  generated  at  A  or  at  D 
so  that  it  is  evident  that  relays  are  desirable  whose  adjustments 
can  be  quickly  changed. 

Reverse  Power. — For  the  protection  of  a  parallel  feeder  system 
or  a  ring  system,  reverse  power  relays  are  necessary  and  these  are 
made  by  the  Westinghouse  Company  in  the  form  of  a  two  ele- 
ment relay,  the  current  element  being  practically  the  same  as 
that  of  the  'CO,'  and  having  the  same  overload  and  time  ele- 
ment characteristics.  In  addition  to  the  current  element  there 
is  a  watt  element  that  closes  a  contact  whenever  the  flow  of 
energy  is  in  a  reversed  direction  from  the  normal  one.  The  cur- 
rent element  closes  its  contacts  on  excess  current  in  either  direc- 
tion, but  the  relay  will  not  function  to  trip  the  circuit  breaker 
unless  the  selective  wattmeter  element  also  functions  due  to  the 
power  being  in  the  reversed  direction. 

While  in  many  cases  transmission  and  distribution  systems 
can  be  readily  sectionalized  by  the  standard  application  of  over- 
load and  reverse  power  relays,  there  are  other  conditions  that 
can  best  be  handled  by  a  balanced  system  of  relays. 

Balanced  System. — This  system,  utilizing  pilot  wire  schemes 
and  standard  overload  relays,  operates  from  the  secondaries 
of  current  transformers  placed  at  two  ends  of  the  feeder,  but  such 
an  arrangement  requires  conductors  to  be  run  between  these 
current  transformers  and,  ordinarily,  on  long  distance  transmis- 
sion lines,  such  an  arrangement  is  not  very  practicable. 

Split  Conductors. — A  split  conductor  scheme  can  often  be 
utilized  to  advantage  where  the  power  to  be  transmitted  is  such 
as  to  required  two  conductors  in  parallel.  In  most  cases,  how- 
ever, an  arrangement  of  balancing  relays  on  parallel  feeders  using 
the  cross  connection  of  reverse  power  relays  will  work  out  to  the 
best  advantage. 

Balanced  Relays. — Such  an  arrangement  is  indicated  in  Fig. 
103,  this  showing  four  circuits  between  a  generating  station  and 
receiving  station.  This  schematic  diagram  has  been  simplified 
by  showing  only  one  phase  on  each  of  the  feeder  circuits.  By 


RELAYS 


163 


reference  to  these  two  figures  it  will  be  noted  that  the  current 
transformers  at  the  generating  station  are  connected  in  series  for 
each  particular  phase  and  similarly  at  the  substation,  and  that 
each  relay,  that  must  be  of  the  reverse  power  (uni-directional) 
type,  is  shunted  across  its  own  current  transformer. 

Generating  Station 


FIG.  103. — Balanced  arrangement  of  relays. 

Under  normal  conditions  the  load  in  each  of  the  parallel  feeders 
will  be  the  same,  and  since  the  relays  have  a  higher  impedance 
than  the  current  transformers,  the  current  from  the  latter  will 
circulate  through  all  of  them  in  series  without  any  flowing  through 
the  relays.  If  the  trouble  occurs  at  any  point  outside  the  section 
protected  by  the  cross  connected  relays,  the  current  over  the 
feeders  will  still  be  balanced  and  consequently  there  will  be  no 
force  tending  to  operate  the  relays.  In  other  words,  a  short 
circuit  occurring  on  some  other  portion  of  the  system  will  have  no 
tendency  to  trip  out  any  of  the  breakers  in  this  section. 

On  the  other  hand  if  trouble  occurs  at  a  point  within  the  pro- 
tected sections,  the  current  over  the  defective  circuits  will  be 
higher  than  that  in  the  others,  and  this  excess  current  from  its 
current  transformer  must  pass  through  the  relays.  While  under 
this  unbalanced  condition,  current  will  flow  through  all  of  the 
relays,  it  will  be  observed  that  the  current  is  in  the  proper  direc- 
tion to  cause  the  relays  to  act  only  at  each  end  of  the  defective 
section  as  shown  by  the  arrows  in  the  diagram. 

Pallet  switches  are  connected  in  the  transformer  secondary 
circuit  and  are  mechanically  operated  by  the  breaker  so  that 
when  the  breaker  opens  the  current  transformers  are  short- 


164        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

circuited.  By  this  method,  a  feeder  can  be  cut  out  of  service 
without  interfering  with  the  electrical  balance  in  the  current 
transformer  circuits. 

Double  Contact  Relays. — Where  there  are  only  two  parallel 
feeder  circuits,  a  double  contact  reverse  power  relay  can  be 
utilized.  This  relay  is  so  arranged  that  in  case  of  trouble,  the 
watt  element  will  close  the  circuit  leading  to  the  trip  coil  of  the 
breaker  in  the  defective  circuit,  and  the  excess  current  element 
will  operate  to  trip  out  that  breaker  under  suitable  conditions 
of  overload  and  time  element. 

More  complicated  networks  can  usually  be  taken  care  of  by 
proper  selection  of  the  type  of  relays  to  be  employed.  It  fre- 
quently happens  that  the  problem  of  automatic  sectionalizing 
can  be  very  much  simplified  if,  at  the  instant  of  short  circuit,  a 
number  of  circuit  breakers  are  opened  for  the  purpose  of  simpli- 
fying the  operation  of  the  remainder  of  the  systems. 

These  induction  type  relays  of  the  Westinghouse  Company 
have  their  characteristic  curves  marked  on  their  nameplates. 
The  corresponding  relays  of  the  General  Electric  Company 
have  the  information  in  the  form  of  tabulated  data  on  their 
nameplates.  All  of  these  induction  type  relays  utilize  many  of 
the  parts  of  the  induction  type  watt-hour  meters  of  the  respective 
makers. 

The  inverse  definite  time  limit  relays  of  the  Condit  Electrical 
Manufacturing  Company  have  many  features  similar  to  those 
mentioned  above,  except  that  they  do  not  use  any  power  con- 
suming retarding  element,  such  as  bellows,  dashpot,  magnetic 
drags,  etc.  The  current  adjustment  is  obtained  by  means  of  a 
calibrated  compression  spring  and  the  time  adjustment  is 
obtained  by  moving  the  contact  arm  into  various  positions  on 
the  worm  wheel. 

The  usual  sectionalizing  relays  are  intended  for  disconnecting 
defective  feeders  and  are  not  primarily  intended  to  protect 
apparatus  in  case  of  overload.  The  current  settings  of  such 
relays  are  generally  a  function  of  the  current  flowing  under  short 
circuit  and  are  thus  higher  than  required  for  protection  against 
sustained  overload. 

Temperature  Relay. — This  may  be  used  to  protect  any  alternat- 
ing current  apparatus  from  excessive  heating  if  the  apparatus  is 
so  arranged  that  exploring  coils  can  be  installed.  The  relay 
is  intended  to  protect  apparatus  against  overheating  from  sus- 


RELAYS  165 

tained  overloads.  To  afford  this  protection  with  the  least 
interruption  of  service  the  breaker  should  be  tripped  through 
the  direct  effect  of  the  temperature  of  the  apparatus.  The 
relay  should  be  so  arranged  that  it  prevents  the  breaker  from 
tripping  if  the  overload  is  of  such  short  duration  that  the  tem- 
perature does  not  rise  to  a  dangerous  value;  while,  if  the  overload 
persists,  the  breaker  must  be  tripped  out  as  soon  as  the  tempera- 
ture rises  beyond  the  critical  value.  This  is  accomplished  as 
follows : 

Principles. — The  temperature  relay  operates  on  the  Wheat- 
stone  bridge  principle.  Two  arms  of  the  bridge  are  copper 
exploring  coils  arranged  to  be  placed  in  the  oil  or  embedded  in 
the  windings  of  the  apparatus  to  be  protected,  the  other  two 
arms  are  unchanging  resistance  mounted  in  the  relay.  The 
current  for  the  bridge  is  supplied  by  the  current  transformer 
connected  in  the  circuit  of  the  apparatus  to  be  protected.  The 
relay  has  two  windings,  corresponding  to  and  co-operating  to 
produce  torque  in  a  manner  similar  to  the  current  and  voltage 
coils  of  a  wattmeter.  The  main  winding  is  a  coil  operated 
directly  by  the  current  transformer.  The  auxiliary  coils  are 
connected  to  the  Wheatstone  bridge  arms  similarly  to  a  galvano- 
meter connection,  and  thus  receive  current  the  magnitude  and 
direction  of  which  depends  upon  the  resistance  of  the  search  coils. 
Above  a  certain  temperature  the  torque  of  the  relay  is  in  the 
contact  direction  and  below,  in  the  opposite  direction.  It  will 
thus  be  noted  that,  in  order  to  close  the  contact,  two  predetermined 
conditions  must  co-exist:  excess  current,  and  excess  temperature. 
Neither  one  will  separately  trip  the  relay. 

Transfer  Relays. — These  are  used  with  protective  relays  that 
operate  on  excess  current  where  a  direct-current  trip  circuit  is 
not  available.  They  energize  the  trip  coil  of  the  circuit  breaker 
through  current  transformers. 

The  breaker  operates  solely  through  the  current  transformer 
and  the  relays.  When  there  is  no  fault  on  the  line  the  trip  coil 
of  the  breaker  is  mechanically  and  electrically  isolated  from  the 
circuit,  avoiding  possibility  of  tripping  due  to  imperfection  in  the 
relay  contacts  ordinarily  shunting  the  trip  coil. 

The  relay  contains  two  series  coils,  an  upper  or  operating  coil 
and  a  lower  or  holding  coil  (see  diagram  of  connections,  Fig.  104). 
The  holding  coil  holds  down  the  armature  core,  until  a  third  coil, 
wound  on  the  same  magnetic  circuit  and  known  as  the  releasing 


166       SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


coil,  is  short-circuited  by  the  protective  relay.  The  releasing 
coil  acts  as  the  secondary  of  a  transformer  and  when  short-cir- 
cuited, a  current  flows  through  it,  demagnetizing  the  core.  The 
holding  coil,  therefore,  allows  the  operating  coil  to  raise  the  core 
which  operates  the  transfer  switch,  thus  closing  the  trip  coil 
circuit. 


FIG.  104. — Transfer  type  relay. 

The  transfer  switch  and  other  current-carrying  parts  of  the 
relay  are  designed  to  carry  5  amperes  continuously,  but  during 
time  of  short  circuit  the  switch  may  be  called  on  to  handle  as 
much  as  100  or  200  amperes. 

A  current  transformer  must  be  selected  of  sufficient  capacity  to 
operate  the  protective  relay,  the  transfer  relay,  and  the  trip  coil. 
Low  ratio  bushing  type  current  transformers  sometimes  used  on 
high  voltage  circuit  breakers  are  not  suitable. 

Only  one  trip  coil  is  required  for  use  on  a  polyphase  circuit,  but 
if  the  breaker  is  equipped  with  as  many  trip  coils  as  there  are 
relays,  it  is  advisable  to  connect  each  trip  coil  to  its  corresponding 
relay. 

Bell  Relay. — This  provides  an  alarm  to  notify  the  attendant 
that  a  circuit  breaker  has  tripped  automatically.  It  is  generally 
mounted  behind  the  switchboard.  This  relay  operates  the  alarm 
when  the  tripping  is  due  to  the  action  of  automatic  tripping 
devices,  but  does  not  operate  when  a  circuit  breaker  is  opened 
intentionally.  The  alarm  can  consist  of  a  bell  or  other  indicating 
device.  The  relay  action  is  such  that  the  alarm  continues  until 
stopped  by  pushing  a  button. 

The  bell  relay  consists  of  a  contact-making  armature  actuated 
by  an  electromagnet  excited  by  two  windings.  One  winding 


RELA  YS 


167 


is  in  series  with  the  automatic  trip  circuit.  When  automatic 
tripping  occurs,  current  passes  through  this  winding  and  the 
armature  is  attracted,  closing  the  bell  circuit.  The  other  winding 
is  in  parallel  with  the  bell  circuit,  so  that  when  the  bell  circuit  is 
closed  this  second  winding  holds  the  armature  and  does  not 
permit  the  circuit  to  open  when  the  trip  circuit  has  opened  with 
the  circuit  breaker.  The  bell  circuit  is  opened  by  means  of  a 
push  button  provided  for  this  purpose,  whereupon  the  armature 
of  the  relay  opens  contact. 


B  A 


To-f  Operating  Bus. 

To  Opening  Wire 
Gen  Oil  Switch. 
Vfre 
itch. 
To  Opening  Wire 
Of  uuy  other  Switch 
which  it  may  be 
desirable  to  Open. 


FIG.  105. — Schweitzer  &  Conrad  multi-circuit  relay. 

S.  &  C.  Relay. — The  multiple  circuit  sensitive  relay  of 
Schweitzer  and  Conrad  is  used  where  it  is  desirable  to  have  a 
relay  that  will  operate  on  very  small  currents  and  yet  have  con- 
tacts that  will  carry  sufficient  current  to  operate  remote-control 
circuit  breakers,  field  circuit  breakers,  blower  motor  circuits  and 
the  like.  This  is  accomplished  by  having  a  relay  provided  with 
a  weighted  arm  that  has  its  weight  just  beyond  the  center  so  that 
very  little  energy  is  needed  to  carry  it  past  the  center  and  allow  it 
to  fall  into  the  position  where  it  will  close  the  necessary  number  of 


168        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

auxiliary  circuits.  This  type  of  relay  can  be  used  to  advantage  in 
connection  with  the  Merz-Price  system  of  differential  protection. 

With  this  scheme,  the  relays  are  connected  between  the  three- 
phase  pilot  wires  and  the  neutral  pilot  wire  connecting  the 
secondaries  of  the  neutral  current  transformers  to  the  secondaries 
of  the  terminal  current  transformers.  The  relays  are  connected 
at  the  electrical  centers  of  the  pilot  wires.  The  balancing  resis- 
tances shown  in  the  diagram  are  necessary  in  order  to  be  able  to 
connect  the'  relays  to  the  pilot  wires  at  the  electrical  center,  as 
in  most  cases  it  would  be  impractical  to  connect  them  midway 
between  the  two  sets  of  current  transformers. 

Connections. — The  scheme  of  connections  shown  in  Fig.  105 
provides  for  only  three  relay  contact  circuits.  A  favorite  ar- 
rangement with  large  generators  is  to  use  a  four-circuit  relay  to 
open  the  two  generator  oil  circuit  breakers,  the  field  circuit 
breaker  and  blower  motor  circuit  breaker. 

With  the  circulating  current  system  of  generator  protection  the 
relays  are  not  affected  by  an  unbalance  of  current  in  the  different 
phases,  or  by  overloads  and  external  short  circuits  no  matter  how 
great,  or  by  reverse  power,  provided  the  connections  are  made  as 
shown  and  the  balancing  resistances  are  of  the  proper  value.  In 
other  words,  the  relays  will  operate  only  in  case  of  a  ground  or 
other  fault  occurring  in  the  generator  windings  or  on  the  leads 
between  the  neutral  current  transformers  and  the  terminal 
current  transformers.  Furthermore,  they  will  operate  on  such 
small  currents  and  so  quickly  that  they  will  disconnect  the 
generator  from  the  system  and  open  the  field  circuit  before 
material  damage  is  done  at  the  point  of  breakdown  and  with  a 
minimum  of  disturbance  to  the  system  itself. 

Series  Relay. — In  high  voltage  stations  requiring  overload 
protection  and  where  the  extra  cost  of  separate  current  trans- 
formers has  prohibited  the  use  of  accurate  relays,  the  high  voltage 
series  relay  shown  in  Fig.  106  has  been  an  economical  substitute 
affording  ample  overload  protection  and  an  approximate  time 
element.  These  relays  have  been  used  chiefly  for  circuits  of  100 
amperes  or  less;  for  heavier  currents  the  use  of  ring  type  current 
transformers  built  around  the  circuit  breaker  bushings  and  op- 
erating induction  relays  will  be  found  more  convenient.  Series 
relays  are  for  indoor  use  and  are  suitable  for  any  frequency. 

The  relay  coil  is  inserted  in  the  high  voltage  line,  but  the 
contacts  and  timing  parts  are  insulated  and  can  be  handled, 


RELA  YS 


169 


adjusted,  or  tested  without  disconnecting  the  feeder.  The  coil 
can  be  mounted  on  a  disconnecting  switch  or  choke  coil  without 
separate  insulators,  and  the  contact  mechanism  mounted  in 
the  position  most  convenient.  A  solenoid  mechanism  operates 
a  timing  and  circuit-closing  element  through  a  wood  rod  or 
micarta  chain  of  such  length 
as  to  provide  ample  insula- 
tion for  the  voltage  in  use. 

Two  forms  of  series  relays 
are  furnished:  inverse  time 
element  and  definite  time 
element.  The  inverse  time 
element  relay  can  be  set  for 
practically  instantaneous 
tripping. 

Inverse  Time. — In  this  re- 
lay the  solenoid  and  chain  are 
opposed  in  their  motion  by 
a  bellows  with  an  adjustable 
valve.  The  valve  has  a  small 
numbered  dial  which  permits 
of  any  setting  between  a 
maximum  time  element  of 
about  20  seconds  at  25  per 
cent,  overload  and  a  mini- 
mum of  about  1  second  at 
the  same  overload.  With 
greater  overload  the  relay 
acts  in  a  shorter  time. 

Definite  Time. — In  this  relay  the  same  kind  of  bellows  and 
valve  are  used  as  for  the  inverse  time  element,  but  the  solenoid 
chain  does  not  act  directly  on  it.  The  core  and  chain  rise 
instantly  when  the  current  reaches  the  tripping  valve,  and 
compress  a  spring.  The  spring  in  turn  acts  on  the  bellows.  If 
the  overload  continues  for  the  time  for  which  the  relay  is  set 
the  tripping  contacts  close.  The  time  required  for  the  spring 
to  close  the  contacts  depends  only  on  the  setting  of  the  valve, 
and  is  entirely  independent  of  the  magnitude  of  the  overload. 
The  relay  can  be  set  for  any  time  element  between  1  and  10 
seconds. 

The  minimum  current  at  which  the  relay  will  trip  depends 


FIG.   106. — Series  type  of  relay. 


170        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


on  the  number  of  weights  placed  on  the  arm  of  the  contact 
making  mechanism.  This  can  be  varied  from  80  per  cent,  to 
160  per  cent,  of  the  rated  current  of  the  relay. 

These  relays  are  not  as  accurate  as  to  time  element  as  the 
magnetically  damped  relays.  Their  time  element  will  be  found 
sufficiently  accurate  to  afford  protection  on  the  circuit  to  which 
applied,  but  selective  protection  with  regard  to  other  circuits  in 
the  system  cannot  always  be  satisfactorily  obtained  with  a 
bellows  relay. 

The  circuit  breaker  should  have  auxiliary  contacts  to  open  the 
trip  circuit  when  the  breaker  opens,  reliev- 
ing the  relay  contacts  of  this  duty. 

One  relay  is  required  to  protect  a  single- 
phase  circuit,  two  relays  for  a  2-phase  or 
3-phase  ungrounded  neutral  circuit,  and 
three  relays  for  a  3-phase  grounded  netural 
circuit. 

An  insulating  support  for  the  relay 
element  is  not  furnished  separately  as  the 
relay  is  intended  to  be  mounted  on  the 
disconnecting  switch  pillar  or  other  support 
of  the  high  voltage  line.  Where  required 
a  bracket  support  complete  with  insulator 
and  necessary  mounting  plate  can  be 
supplied. 

High  Voltage  Induction. — Fig.  107  shows 
the  latest  modification  in  this  type  of  equip- 
ment where  the  series  solenoid  is  replaced 
by  a  low  voltage  series  transformer,  an 
accurate  induction  type  relay  and  a  transfer 
type  relay,  all  of  these  devices  being 
mounted  on  a  small  panel,  the  latter  being 
supported  by  a  high  voltage  insulator.  The  current  transformer 
and  induction  relay  permit  very  accurate  relay  settings  with  ad- 
justable definite  time  delay  from  0.1  to  2  seconds,  and  current 
settings  from  4  to  12  amperes.  The  operation  of  the  induction 
relay  serves  to  close  the  circuit  of  the  releasing  coil  of  the  transfer 
relay.  This  transfer  relay  is  connected  through  a  micarta  in- 
sulating chain  to  the  switch  whose  contacts,  on  closing,  cause 
the  electrical  tripping  of  the  breaker. 

With  certain  changes  this  type  of  relay  has  been  made  suitable 
for  outdoor  high  voltage  service. 


FIG.  107. — Westing- 
house  high  voltage 
induction  type  relay. 


CHAPTER  VI 
SWITCHBOARD  METERS 

While  this  chapter  deals  particularly  with  instruments,  their 
detail  design  will  not  be  touched  on  but  some  general  information 
will  be  given  relative  to  meters  and  their  various  functions  in 
connection  with  switchboards. 

Compactness. — This  is  one  of  the  essential  features  of  switch- 
board meters  owing  to  cost  of  panel  space,  reduction  in  attendance 
and  visibility  of  all  instruments  from  one  point  of  operation. 
While  securing  compactness,  length  of  scale  has  not  been  lost 
sight  of  in  design  and  this  length  of  scale  varies  greatly  in  instru- 
ments of  different  designs  occupying  approximately  the  same 
amount  of  space. 

Accuracy. — While  this  is  of  great  importance  it  is  necessary 
to  distinguish  between  the  accuracy  that  is  desired  in  laboratory 
instruments  and  the  accuracy  which  can  be  obtained  in  switch- 
board meters  without  sacrificing  other  essential  qualities  such 
as  ruggedness,  sensibility  and  accessibility.  For  switchboard 
work  it  is  better  to  secure  instruments  that  will  stay  accurate 
within  2  per  cent,  with  an  initial  error  of  1  per  cent,  than  to 
use  meters  whose  initial  error  is  only  a  small  fraction  of  1  per 
cent,  but  which  will  not  remain  within  2  per  cent,  when  used  in 
actual  switchboard  work  where  the  magnetic  stresses  resulting 
from  system  short  circuits  are  apt  to  damage  a  very  sensitive 
meter.  High  accuracy  and  ruggedness  are  more  or  less  antago- 
nistic qualities  and  a  satisfactory  compromise  is  an  initial  error 
of  about  1  per  cent,  and  a  final  error  in  actual  service  of  less 
than  2  per  cent. 

D.C.  Meters. — For  direct-current  service  the  cheaper  grades 
of  meters  are  made  of  the  moving  iron  type  while  the  better 
grade  of  ammeters  and  voltmeters  are  of  the  D'Arsonval  per- 
manent magnet  construction.  When  the  meters  are  so  designed 
that  the  movements  can  be  readily  removed  without  disturbing 
the  magnetic  circuit  by  the  removal  of  the  pole  pieces  they  are 
particularly  suitable  for  switchboard  service. 

171 


172        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

A.C.  Meters. — For  A.C.  service  the  indicating  instruments  are 
made  as  "moving  iron,"  "moving  coil"  or  "induction"  type 
and  the  relative  advantages  and  disadvantages  of  these  types 
are  as  follows: 

Moving  Iron. — This  electromagnetic  type  of  meters  has 
good  initial  accuracy  and  is  approximately  free  from  tempera- 
ture and  frequency  errors  and  is  easy  to  repair.  Unless 
heavily  shielded  they  are  subject  to  external  fields  and  their 
scale  length  is  short. 

Moving  Coil. — This  electrodynamometer  type  is  free  from 
errors  due  to  temperature  and  frequency  variation  and  can  be 
made  with  very  high  initial  accuracy.  They  are  usually  delicate 
and  difficult  to  repair,  have  short  scale  lengths  and  are  subject 
to  external  fields  of  same  frequency  unless  heavily  shielded  by 
internal  laminated  iron  shields. 

Induction  Type. — These  meters  have  good  initial  and  service 
accuracy,  rugged  and  simple  movements,  extremely  long  and 
easily  read  scales  and  are  easy  to  repair.  The  frequency  error  is 
greater  than  in  the  other  types  and  they  are  subject  to  slight 
errors  from  external  fields  only  when  of  the  same  frequency  and 
in  certain  directions. 

D.C.  Ammeters. — Direct-current  ammeters  of  the  moving 
iron  type  are  built  for  connecting  directly  in  the  circuit  in  capaci- 
ties up  to  about  600  amperes  while  the  permanent  magnet 
meters  are  made  in  all  capacities  and  are  usually  operated  from 
shunts  having  a  drop  of  approximately  50  millivolts. 

D.C.  Voltmeters. — D.C.  voltmeters  of  any  type  are  connected 
directly  across  the  circuit  in  series  with  a  resistance  or  are  con- 
nected across  a  portion  of  the  resistance  in  such  a  way  that  their 
scale  reading  gives  a  correct  indication  of  the  pressure.  As 
most  D.C.  plants  whether  for  railway  or  for  light  and  power 
service  are  operated  at  practically  constant  potential  the  volt- 
meters are  depended  on  as  a  guide  to  the  operators  in  maintaining 
the  proper  pressure. 

A.C.  Voltmeters. — These  are  usually  wound  for  connecting 
directly  to  the  circuit  for  pressures  up  to  approximately  750 
volts  and  beyond  that  point  are  operated  from  voltage  trans- 
formers usually  with  a  100-volt  secondary.  These  voltmeters 
are  frequently  marked  with  scale  corresponding  to  primary  volt- 
age of  the  transformers,  and  have  coils  that  will  stand  150 
volts.  For  example,  the  voltmeter  used  with  the  6600-volt  cir- 


SWITCHBOARD  METERS  173 

cuit  would  probably  be  operated  from  a  transformer  having  a 
ratio  of  6600-110  volts  and  would  be  provided  with  a  scale  of 
9000  volts. 

A.C.  Ammeters. — Certain  types  are  made  in  capacities  up 
to  about  300  amperes  for  connecting  directly  in  the  circuit 
unless  the  voltage  is  high,  but  the  better  grades  of  instruments 
are  operated  from  current  transformers  usually  having  a  sec- 
ondary current  of  5  amperes.  The  scale  reading  of  the  meter  is 
usually  made  to  correspond  with  the  primary  capacity  of  the 
current  transformer.  Arrangements  can  usually  be  made  so 
that  one  A.C.  ammeter  can  be  operated  from  any  number  of 
current  transformers,  so  as  to  read  the  current  in  any  circuit. 

Wattmeters. — On  A.C.  generator  panels  and  sometimes  on 
other  panels  of  a  switchboard,  indicating  wattmeters  are  desirable 
to  show  at  a  glance  the  output  of  that  particular  circuit  indepen- 
dent of  the  voltage  or  power  factor  of  the  circuit.  They  are 
particularly  useful  on  A.C.  generator  panels  to  facilitate  the 
proper  division  of  the  load.  On  panels  for  use  with  synchronous 
motor-generator  sets  or  tie  circuits  which  may  either  be  taking 
power  from  or  delivering  power  to  the  bus  bars,  double  reading 
wattmeters  with  the  zero  in  the  center  of  the  scale  are  recom- 
mended. 

Watt-hour  Meters. — On  feeder  and  load  panels  and  sometimes 
on  generator  panels  it  is  often  deemed  advisable  to  install  watt- 
hour  meters  either  A.C.  or  D.C.  to  record  the  power  supplied  to 
a  certain  feeder,  to  one  set  of  bus  bars  or  furnished  by  one  genera- 
tor. A.C.  watt-hour  meters  can  be  provided  with  a  recording 
demand  chart  to  give  readings  every  15  minutes. 

Power  Factor. — On  panels  for  control  of  the  A.C.  end  of 
synchronous  converters  and  synchronous  motors  it  is  advisable  to 
install  power  factor  meters  or  reactive  factor  meters  as  these 
instruments  will  show  at  a  glance  whether  the  fields  have  been 
adjusted  to  best  advantage  or  whether  the  current  taken  is 
leading  or  lagging  in  character.  As  the  pointer  on  one  design 
of  the  power  factor  meter  can  move  through  an  arc  of  360  degrees 
it  can  indicate  whether  the  circuit  in  which  it  is  connected  is 
delivering  power  to  or  taking  power  from  the  bus  and  whether  the 
current  is  leading  or  lagging. 

Field  Ammeters. — These  are  often  supplied  for  use  in  con- 
nection with  generator  and  synchronous  motor  circuits  to  aid  in 
the  proper  adjustment  of  the  field. 


174        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Frequency  Meters. — These  can  often  be  used  to  advantage  to 
determine  the  frequency  at  which  the  plant  is  operating.  Where 
there  are  two  or  more  sets  of  bus  bars,  or  several  stations  feeding 
into  a  common  transmission  line  this  point  is  often  of  vital 
importance. 

Synchronoscopes. — On  the  better  class  of  A.C.  boards  it  is 
usual  to  supply  synchronoscopes  instead  of  depending  on  lamps 
for  synchronizing.  These  instruments  of  General  Electric 
or  Westinghouse  make  are  so  made  as  to  actuate  a  hand  moving 
around  a  dial  in  such  a  manner  that  the  angle  between  the  pointer 
and  the  vertical  indicates  the  phase  angle  between  the  E.M.F. 
of  the  bus  bars  and  the  machine  to  be  connected.  If  the  fre- 
quency of  the  incoming  machine  is  too  high,  i.e.,  if  the  machine 
is  running  too  rapidly  the  pointer  will  revolve  in  the  direction 
marked  "fast"  while  if  the  machine  is  not  running  rapidly  enough 
the  pointer  will  revolve  in  the  direction  marked  "slow." 

The  synchronoscopes  of  the  Weston  Electrical  Instrument 
Company  are  built  on  a  different  principle  resulting  in  the  ap- 
parent movement  of  the  hand  across  the  scale  in  one  direction  or 
the  other  corresponding  to  the  "fast"  or  "slow"  direction  with 
the  pointer  stationary  at  the  middle  of  the  scale  at  the  instant  of 
synchronism. 

Static  Ground  Detectors. — For  higher  voltages  static  ground 
detectors  are  recommended.  The  Westinghouse  types  are 
operated  from  condensers  so  that  there  is  no  danger  from  high 
voltage  in  the  instruments,  in  case  of  accidental  contact.  With 
the  General  Electric  device,  rods  of  high  resistance  material 
limit  the  current  to  an  inappreciable  amount  in  case  of  accidental 
contact. 

Graphic  Meters.— In  addition  to  the  indicating  meters  de- 
scribed above  various  manufacturers  furnish  D.C.  ammeters  and 
voltmeters  as  well  as  A.C.  ammeters,  voltmeters,  wattmeters, 
power  factor  meters  and  frequency  meters  that  plot  a  graphic 
chart  either  as  a  circular  chart  with  polar  co-ordinates  or  on  a 
continuous  strip  with  rectilinear  co-ordinates.  In  the  first 
case  circular  charts  about  8  inches  in  diameter  are  used,  revolving 
once  an  hour  or  once  a  day  or  at  some  other  predetermined  rate 
while  with  the  latter  type  the  scale  on  the  chart  moves  at  2, 
4,  8  inches  per  hour  or  at  any  other  desirable  speed  and  a  record 
for  a  month  or  so  can  be  made  on  a  continuous  strip  of  paper  if 
desired. 


SWITCHBOARD  METERS 
GENERAL  ELECTRIC  INSTRUMENTS 


175 


Horizontal  Edgewise. — The  indicating  instruments  of  the 
General  Electric  Company  are  made  in  various  forms  but  the 
usual  design  for  use  on  large  A.C.  switchboards  is  the  horizontal 
edgewise  arrangement  illustrated  in  Fig.  108.  These  instruments 


FIG.  108. — General  Electric  Co.  horizontal  edgewise  meter. 

are  about  6^  inches  high,  8  inches  wide  and  all  of  the  usual  types 
of  indicating  meters  both  A.C.  and  D.C.  are  made  in  this  form, 
presenting  a  very  uniform  appearance  on  a  switchboard.  The 
A.C.  meters  are  operated  from  current  and  potential  trans- 
formers and  the  D.C.  ammeters  either 
direct  in  the  circuit  for  moderate 
capacities  or  operated  from  shunts  in 
the  larger  sizes.  These  meters  are 
very  substantial  in  their  construction 
and  withstand  well  the  short-circuit 
stresses  met  with  in  actual  station 
operation. 

Round  Pattern. — Round  pattern 
meters  are  made  as  ammeters  and 
voltmeters  for  A.C.  and  D.C.  service 
in  two  sizes,  one  about  9^  inch  and 
the  other  7>^  inch  diameters.  The  D.C.  instruments  work  on 
the  D'Arsonval  principle,  while  the  A.C.  instruments  work  on 
the  Thomson  inclined  coil  principle,  the  appearance  of  these 
meters  being  as  shown  in  Fig.  109. 

D.  C.  Watt-hour  Meters. — All  G.  E.  direct-current  switchboard 
watt-hour  meters  are  essentially  high  torque  devices.     Friction 


FIG.  109. — General  Electric  Co. 
round  pattern  meter. 


176        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

is  reduced  to  lowest  value  and  ratio  of  torque  to  friction  is  maxi- 
mum, insuring  long  life  with  continued  accuracy.  The  design 
of  the  commutator  and  bearings  is  such  that  the  possibilities 
of  increased  friction  due  to  age  and  wear  are  minimized,  hence  the 
ratio  of  torque  to  friction  increases,  which  is  the  real  criterion  of 
the  accuracy  of  a  meter,  is  very  large. 

Having  no  iron  in  armature  or  field  circuits,  no  considerations 
of  magnetic  saturation  are  involved.  Therefore,  meters  have 
straight-line  characteristics  even  to  point  of  physical  destruction. 

The  armatures  of  the  D.C.  watt-hour  meters  are  spherical 
and  move  in  a  circular  field.  This  secures  highest  torque  with 
lowest  watt  loss,  the  greatest  possible  number  of  magnetic  lines 
being  cut  by  the  armatures.  Their  astatic  arrangement  mini- 
mizes effect  of  stray  fields  since  any  magnetic  field  tending  to 
weaken  the  torque  of  one  armature  strengthens  torque  of  the  other. 

A.C.  Watt-hour  Meters. — These  meters  for  switchboard 
service  are  rectangular  in  shape  and  provided  with  metal  cover 
or  glass  cover  and  arranged  for  single  phase  or  polyphase  service. 
These  meters  are  provided  with  testing  terminals  that  allow 
testing  meters  to  be  cut  into  the  circuit  or  the  meter  winding 
isolated  without  interrupting  the  circuit  or  without  going  behind 
the  switchboard.  The  corresponding  house  meters  for  single 
phase  or  polyphase  service  are  provided  with  metal  covers. 

Round  pattern  curve  drawing  instruments  are  provided  with 
electrical  elements  of  the  solenoid  type,  direct  acting  with  gravity 
control.  Charts  are  circular  8-inch  diameter  with  a  chart  speed 
of  one  revolution  in  either  12  or  24  hours,  but  other  speeds  can 
be  furnished. 

Large  graphic  meters  with  a  rectangular  chart  about  5  inches 
wide  and  a  paper  speed  of  3  or  6  inches  per  hour  can  be  supplied 
as  ammeters,  voltmeters,  indicating  wattmeters,  power  factor 
meters,  frequency  meters,  etc. 

BRISTOL,  ESTERL1NE,  DUNCAN,  SANGAMO  METERS 

A  complete  line  of  graphic  instruments  are  made  by  the  Bristol 
Company  embracing  the  usual  ammeters,  voltmeters,  and  watt- 
meters, as  well  as  recording  thermometers,  pressure  gauges  and 
other  similar  devices.  The  Esterline  Company  build  graphic 
instruments  of  all  kinds,  while  shunt  type  D.C.  watt-hour  meters 
are  made  by  the  Duncan  and  by  the  Sangamo  companies.  Space 
does  not  permit  a  description  of  them. 


SWITCHBOARD  METERS  177 

THE  ROLLER   SMITH   COMPANY 

The  Roller  Smith  Company  make  indicating  instruments  in 
various  sizes  and  shapes  for  D.C.  and  A.C.  work  to  measure 
current,  voltage,  etc. 

For  direct-current  work  for  batteries  and  automobile  work, 
ammeters  up  to  100  amperes  and  voltmeters  up  to  150  volts  are 
made  with  an  over-all  diameter  of  3^  inches  and  body  diameter 
of  2%  inches  in  either  the  protruding  or  flush  styles  of  mountings. 
These  instruments  are  of  the  permanent  magnet  moving  coil 
type  with  light  but  rigid  moving  elements.  These  are  known  as 
"Junior  Imps. " 

The  4-inch  Imps  are  made  as  ammeters  up  to  200  amperes  and 
as  voltmeters  up  to  300  volts.  These  instruments  are  4  inches  in 
diameter  of  the  moving  coil  type. 

Junior  and  4-inch  Imp  instruments  are  made  as  A.C.  ammeters, 
voltmeters  and  single-phase  wattmeters.  The  ammeters  and 
voltmeters  are  of  the  electromagnetic  type  while  the  single-phase 
and  D.C.  wattmeters  are  of  the  electrodynamometer  type.  A 
very  efficient  air  damping  scheme  is  used. 

The  standard  D.C.  switchboard  ammeters  and  voltmeters 
are  made  in  7^-inch  and  9-inch  round  pattern  protruding  or 
flush  type  and  illuminated  dial.  These  meters  can  be  furnished 
with  the  usual  ranges  and  are  all  of  the  permanent  magnet  mov- 
ing coil  D'Arsonval  type.  Horizontal  edgewise  ammeters  and 
voltmeters  can  also  be  furnished. 

A.C.  instruments  can  be  supplied  in  the  7^-inch  and  9-inch 
round  patterns  and  illuminated  dial  types,  the  mechanism  being 
the  electromagnetic  type  air  damped  for  the  ammeters  and  volt- 
meters. Ammeters  and  voltmeters  can  also  be  supplied  in  the 
horizontal  edgewise  construction.  Power  factor  meters,  fre- 
quency meters,  indicating  wattmeters,  synchronoscopes  and 
ground  detectors  can  also  be  furnished. 

Recording  Synchronoscope. — A  recording  device  made  by 
Schweitzer  and  Conrad,  for  attaching  to  a  synchronoscope  consists 
essentially  of  a  paper  holding  and  shifting  device,  and  insulated 
ring  in  the  synchronoscope  dial  and  a  spark  coil  or  vibrator.  A 
continuous  ribbon  of  paper  is  fed  from  a  metal  spool  on  the  left 
along  guides  and  across  the  upper  half  of  the  synchronoscope  dial 
to  the  spool  on  the  right. 

The  dial  plate  of  the  ordinary  synchronoscope  is  replaced  by 
one  of  insulating  material  having  a  brass  ring  set  in  flush  with  its 
surface.  The  ring  has  a  radius  a  little  less  than  the  length  of  the 


178        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

instrument  pointer  and  is  furnished  with  an  insulated  stud  extend- 
ing through  the  back  of  the  indicator  case.  To  the  under  side 
of  the  pointer  and  directly  in  line  with  the  ring  is  attached  a 
platinum  point. 

One  of  the  leads  from  the  spark-coil  secondary  is  connected  to 
the  insulated  stud,  and  the  other  to  a  stud  screwed  into  the  instru- 
ment case  and  therefore  is  in  electrical  connection  with  the 
pointer.  The  primary  leads  are  connected  to  a  direct-current 
source,  such  as  the  exciter  or  operating  bus,  through  an  auxiliary 


Bemoved.'  From  To  Oil 

Pot. Trans.  Switch 

FIG.  110. — Connections  of  Schweitzer  &  Conrad  record  synchronoscope. 

contact  the  location  of  which  depends  upon  the  scheme  of  control 
wiring.  The  purpose  of  the  auxiliary  contact  is  to  close  the 
circuit  to  the  spark-coil  primary  simultaneously  with  the  closing 
of  the  control  switch  and  to  keep  it  closed  until  opened  by  the 
operator. 

The  connections  of  this  device  are  shown  in  Fig.  110.  With 
the  energizing  of  the  spark  coil  at  the  time  the  control  switch  is 
closed,  a  succession  of  sparks  jump  from  the  insulated  ring  to  the 
electrode  on  the  pointer,  puncturing  the  paper  ribbon  and  so  form- 
ing the  record.  For  a  perfect  operation  the  record  will  be  a  very 
short  row  of  quite  large  punctures.  These  will  be  all  on  one 


SWITCHBOARD  METERS  179 

side  of  the  synchronous  position  if  the  machine  was  running 
faster  than  the  system  frequency  and  all  on  the  other  side  if  slower. 

WESTINGHOUSE  INSTRUMENTS 

As  typical  of  a  complete  line  of  instruments,  the  various  types 
made  by  the  Westinghouse  Electric  &  Manufacturing  Company 
will  be  enumerated  in  considerable  detail. 

Small  D.C. — For  automobile  service  the  type  El  ammeters 
have  2-inch  dials  and  IJ^-inch  scales,  while  the  type  EW  instru- 
ments are  made  as  ammeters  and  voltmeters  with  3-inch  dials 
and  2%-inch  scales. 

Type  El. — This  instrument  utilizes  the  polarized  vane  con- 
struction, comprising  a  moving  soft-iron  vane  polarized  by 
a  stationary  permanent  magnet  and  deflected  over  its  scale  by  the 
action  of  a  stationary  current  coil.  No  springs  or  moving  coils 
are  used,  thus  resulting  in  great  simplicity  and  ruggedness.  The 
indications  are  made  deadbeat  by  means  of  an  efficient  damper. 

Type  EW. — The  instrument  operates  on  the  D'Arsonval 
principle,  involving  a  permanent  magnet  and  a  moving  coil,  with 
spiral  current-carrying  springs,  mounted  in  pivot  and  jewel 
bearings;  the  movement  being  rendered  deadbeat  by  winding  the 
moving  coil  on  an  aluminum  damping  frame. 

Both  types  of  these  meters  are  mounted  in  open-faced  circular 
pressed-metal  cases  arranged  with  a  flange  for  flush  mounting. 

For  use  where  small  size  is  essential,  the  types  BX,  AW,  EH 
and  FW  instrument  designs  are  well  adapted. 

Type  BX. — These  instruments  for  direct  current  or  alternating 
current  of  any  frequency  have  2-inch  dials,  2-inch  scales  and  they 
may  be  used  for  the  measurement  of  small  direct  currents,  such  as 
the  filament  and  plate  currents  of  radio  communication  sets,  or  on 
farm-lighting  or  other  small  charging  and  lighting  panels,  or  in 
dental,  electro-medical,  or  other  applications  where  space, 
economy  and  accuracy  are  essential. 

Type  BX  instruments  operate  on  the  D'Arsonval  principle. 
By  combining  the  millivoltmeter  with  a  noninductive  heater  and 
thermocouple  it  is  made  suitable  for  the  measurement  of  high 
frequency  alternating  currents  such  as  are  encountered  in  radio 
communication.  The  same  instrument  may  also  be  operated 
on  alternating-current  circuits  of  commercial  frequency. 

Type  AW. — The  type  AW  switchboard  instruments  for  direct 
current  are  3  inches  in  diameter  with  2%-inch  scales  and  are 


180        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

especially  suitable  for  use  on  small  direct-current  switchboard 
panels,  such  as  battery  charging,  generator  and  control  panels 
for  marine,  dental,  telegraph,  telephone  and  farm  lighting 
equipments.  The  D'Arsonval  type  of  movement  is  employed, 
using  a  case  with  a  round  open-face,  glass  cover,  with  rear  mount- 
ing studs,  stamped  metal  case  and  rim. 

These  instruments  are  guaranteed  to  be  correct  within  2  per- 
cent of  full  scale  at  all  parts  of  the  scale,  and  are  3^  inches  in 
diameter  over  all  and  project  1%  inches  from  face  of  panel; 
studs  suitable  for  panels  up  to  %  inch  thick. 

Type  FW. — The  type  FW  switchboard  instruments  for  direct 
current  are  5  inches  diameter  with  4-inch  scales  and  are  similar 
in  main  features  to  the  type  AW. 


FIQ.  111. — Westinghouse  D.C.  instruments — comparison  white  and  black  dials. 

Seven-inch  Meters. — For  most  of  the  important  switchboards 
built  by  the  Westinghouse  Company  they  utilize  the  7-inch 
diameter  meters  known  as  type  SL  for  D.C.  service  and  SM,  SI,  or 
SD  for  A.C.  These  meters  are  made  either  with  the  usual  white 
dials  and  black  figures  or  with  black  dials  having  white  figures. 
The  relative  legibility  of  the  two  different  types  of  dials  with  the 
same  illumination  is  shown  in  Fig.  Ill,  where  a  lamp  directly 
above  and  between  two  meters  is  provided  with  a  half  shade  to 
throw  the  light  directly  on  the  dial  of  each  meter. 

D.C.  INSTRUMENTS 

Type  SL. — These  switchboard  ammeters  and  voltmeters  for 
direct  current  are  intended  for  the  most  general  switchboard 
applications,  wherever  highest  grade  instruments  are  required. 
Their  cases  are  of  soft  iron,  easily  removed,  the  base  remaining 
on  the  panel,  and  they  are  provided  with  covers  of  flat  glass 
rendering  the  entire  pointer  visible;  this  makes  it  easy  to  take 


SWITCHBOARD  METERS  181 

readings  from  a  distance  and  from  any  angle.  The  scales  are 
approximately  7  inches  long  and  the  meters  operate  on  the 
D'Arsonval  principle,  but  have  a  moving  coil  operating  in  a 
single  air  gap.  The  complete  movement  is  readily  removed  for 
repairs.  The  single  air  gap  construction  makes  it  possible  to 
remove  the  moving  coil  without  first  removing  the  pole  pieces  and 
without  disturbing  in  any  way  the  magnetic  circuit. 

Voltmeters. — The  resistance  of  the  voltmeters  is  approximately 
50  ohms  per  volt  up  to  750  volts.  For  higher  voltages  the 
resistance  is  100  ohms  per  volt.  The  accuracy  is  1  percent  of 
full  scale  at  points  between  %  and  %  scale,  and  average  accuracy 
2  percent  of  full  scale  at  other  points.  These  instruments  have 
an  over-all  diameter  7^6  inches;  depth  from  switchboard,  4 
inches. 

Ammeters. — With  the  exception  of  the  self-contained  styles, 
type  SL  ammeters  operate  from  shunts  and  give  full  scale  de- 
flection with  50  millivolt  drop  at  the  terminals  of  the  shunt. 

Pyrometry  rmllivoltmeters  for  use  with  thermo-electric  couples 
can  be  adjusted  for  20  to  100  millivolts,  full  scale.  The  current 
required  at  full  scale  is  0.01  amperes.  The  scale  can  be  cali- 
brated in  millivolts  or  degrees. 

For  temperature  indicators  voltmeters  arranged  as  resistance 
type  temperature  indicators,  complete  with  coils  or  bulbs,  can  be 
furnished  for  reading  the  temperature  of  machinery,  ovens,  etc. 
The  scale  can  be  calibrated  in  volts  or  degrees. 

Type  SM. — The  A.C.  instruments,  switchboard  ammeters, 
voltmeters  and  wattmeters  for  alternating  current  have  an 
over-all  diameter  of  7%6  inches;  depth  from  switchboard 
4  inches  (the  polyphase  wattmeter  requires  hole  7^6  inches 
diameter  through  panel)  with  14^-inch  scales. 

Type  SM  instruments  operate  on  the  induction  principle, 
with  two  A.C.  fields  so  displaced  that  they  produce  a  rotating 
magnetic  field  that  causes  an  aluminum  drum  to  tend  to  rotate. 
This  tendency  to  rotation  is  opposed  by  a  spiral  spring. 

The  complete  movement  is  readily  removed  for  repairs.  The 
moving  element  consists  of  a  light  drum  and  a  pointer,  both  of 
aluminum,  mounted  on  an  aluminum  shaft,  with  removable 
steel  pivots. 

The  ammeters  and  voltmeters  are  guaranteed  to  be  correct 
within  1  percent  of  full  scale  at  all  points  of  the  scale;  the 


182        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

wattmeters  within  2  percent.     The  general  appearance   of  this 
meter  is  shown  in  Fig.  112. 

Type  SI. — Other  instruments  of  the  induction  type  operating 
on  a  somewhat  different  principle  are  the  type  SI  power  factor 
meters,  reactive  factor  meters  and  synchronoscopes,  the  power 
factor  meter  being  shown  in  Fig.  113.  These  operate  on  the 
rotating  field  principle.  In  the  rotating  field  produced  by  coils 
connected  to  the  metered  circuits  there  is  pivoted  a  movable 
iron  vane  or  armature,  magnetized  by  a  stationary  coil  the  current 
for  which  is  taken  from  a  current  transformer  in  one  phase  of 
the  circuit.  As  the  iron  vane  is  attracted  or  repelled  by  the 
rotating  field,  it  takes  up  a  position  where  the  zero  of  the  rotating 
field  occurs  at  the  same  instant  as  zero  of  its  own  field.  Thus 
its  position  indicates  the  phase  angle  between  the  voltage  and 
current  of  the  circuit. 


FIG.  112.— Westing- 
house  type  S.M.  A.C. 
ammeter. 


FIG.  113. — Westing- 
house  power  factor  in- 
dicator. 


In  the  3-phase  instrument  the  rotating  field  is  produced  by 
three  voltage  coils  spaced  120  electrical  degrees  apart;  and  in 
the  single-phase  instrument  by  means  of  a  split  phase  winding 
connected  to  the  voltage  circuit. 

The  instruments  are  enclosed  in  round,  dust-proof  cases. 
There  are  no  movable  coils  or  flexible  connections  and  no  springs 
are  used  to  control  the  movement.  The  construction  is,  therefore, 
extremely  simple  and  rugged.  External  fields  can  not  influence 
the  readings. 

Synchronoscope. — The  type  SI  synchronoscope  indicates  by 
means  of  a  pointer,  which  assumes  at  every  instant  a  position 
corresponding  to  the  phase  angle  between  the  E.M.Fs.  of  the 
bus  bars  and  the  incoming  machine.  It  gives  exact  indications 


SWITCHBOARD  METERS  183 

and  pointer  is  continuously  visible  during  both  the  dark  and 
the  light  periods  of  the  synchronizing  lamps. 

The  principle  of  operation  is  a  rotating  field  produced  by 
current  from  the  bus  bars  passing  through  a  split  phase  winding 
and  two  angularly  placed  coils.  In  this  rotating  field  is  a  mov- 
able iron  vane,  or  armature,  magnetized  by  a  stationary  coil 
connected  across  the  incoming  machine.  The  iron  vane  takes 
a  position  where  the  zero  of  the  rotating  field  occurs  at  the  same 
instant  as  the  zero  of  the  stationary  field.  Thus  its  position  at 
every  instant  indicates  the  phase  angle  between  the  voltage  of 
the  incoming  machine  and  that  of  the  bus  bars.  As  this  angle 
changes,  due  to  difference  in  frequency,  the  iron  vane  with  the 
pointer  attached  to  it  rotates,  and  when  synchronism  is  reached 
it  remains  stationary. 

Frequency  Meter. — Still  another  induction  type  instrument  is 
the  type  SD  switchboard  frequency  meter.  The  instrument, 
which  operates  on  the  induction  principle,  consists  of  two  volt- 
meter electromagnets  acting  in  opposition  on  a  disk  attached  to 
the  pointer  shaft.  One  of  the  magnets  is  in  series  with  a  reactor 
and  the  other  with  a  resistor,  so  that  any  change  in  the  fre- 
quency will  unbalance  the  forces  acting  on  the  shaft  and  cause 
the  pointer  to  assume  a  new  position  where  the  forces  are  again 
balanced.  The  aluminum  disk,  acted  upon  by  the  magnets,  is 
so  arranged  that  when  the  shaft  turns  in  one  direction  the  torque 
of  the  magnet  tending  to  rotate  it  decreases,  while  the  torque 
of  the  other  magnet  increases.  The  pointer,  therefore,  comes  to 
rest  where  the  torques  of  the  two  magnets  are  equal.  This 
arrangement  insures  freedom  from  error  due  to  varying  voltage. 

Illuminated  Dials. — Where  illuminated  dial  instruments  are 
wanted  they  can  be  supplied  for  either  D.C.  or  A.C.  service. 
The  direct-current  instruments  operate  on  the  D'Arsonval  prin- 
ciple and  alternating-current  instruments  on  the  induction  prin- 
ciple. The  movements  are  similar  to  these  of  the  corresponding 
round  type  instruments.  The  scales  are  15^  inches  long,  and 
are  made  of  translucent  material,  illuminated  from  the  rear  by 
two  110- volt  6-candlepower  tubular  lamps. 

The  D.C.  voltmeters  and  ammeters  are  guaranteed  correct 
within  1  percent  of  full  scale  at  all  points.  The  A.C.  volt- 
meters are  guaranteed  to  be  correct  within  1>^  percent  of 
full  scale  at  all  points;  ammeters  2  percent  at  all  points. 

These   instruments  have  the  following  dimensions:  Over-all 


184        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


height,  12^  inches;  over-all  width,  15%  inches;  depth  3  to 
3^  inches;  mounting  screws  suitable  for  switchboards  up  to  2 
inches  thick. 

Glow  Meters. — The  electro-static  glow  meter  is  a  vacuum 
tube  type  of  electrostatic  potential  indicator  that  may  be  used 
for  indication  of  potential  on  the  line,  as  a  ground  detector 
connected  as  shown  in  Fig.  114  or  as  an  electro-static  synchronism 
indicator  connected  as  shown  in  Fig.  115. 


FIG.  114. — Glow  meter 
connected  as  ground  de- 
tector. 


FIG.     115. — Glow   meter    connected    as    syn- 
chronoscope. 


The  indicating  device  consists  of  three  small  bulbs  filled  with  a 
rare  gas  which  gives  out  a  vivid  orange-red  glow  on  an  extremely 
small  static  discharge,  such  as  can  be  obtained  over  one  section 
of  a  multi-section  line  insulator.  The  base  of  the  instrument  is 
of  micarta  and  the  bulbs  are  mounted  between  spring  clips  and 
are  separated  from  each  other  by  micarta  tubing  which  forms 
barriers  for  the  light  from  the  individual  bulbs. 

This  instrument  utilizes  the  electrostatic  discharge  of  one 
section  of  an  insulator  column.  When  used  as  a  ground  detec- 
tor one  bulb  is  in  parallel  with  the  bottom  section  of  each  of  the 
three  insulator  columns. 

Static  Synchronizer. — When  used  for  synchronizing,  the  phase 
connections  through  the  top  lamps  are  so  made  that  the  lamp  will 
be  out  at  synchronism.  The  phases  of  the  two  lower  lamps  are 
crossed  so  that  they  glow  at  synchronism.  When  out  of  phase 
60  degrees,  all  three  lamps  have  about  half  voltage  impressed  on 
them  and  glow  with  the  same  brilliancy;  when  out  of  phase  120 
degrees,  one  of  the  bottom  lamps  is  out  and  the  other  bottom  lamp 
and  the  top  one  are  glowing.  If  the  two  circuits  are  out  of 
synchronism  there  will  be  an  apparent  rotation  of  the  light  in 
such  a  direction  as  to  show  whether  the  incoming  line  is  fast 
or  slow. 


SWITCHBOARD  METERS 


185 


Watt-hour  Meters. — The  type  OA  watt-hour  meters  shown  in 
Fig.  116  operate  on  the  induction  principle.  The  torque  that  ro- 
tates the  disk  is  proportional  to  the  product  of  voltage,  current 
and  power  factor  of  the  circuit,  and  is  counter  balanced  by  a 
retarding  force  exactly  proportional  to  the  speed.  The  speed  of 
rotation  is,  therefore,  proportional  to  the  power  in  the  circuit. 

Polyphase  type  OA  meters  are  in  reality  two  single  phase  meter 
elements  supported  on  one  mounting  frame,  both  moving  ele- 
ments being  mounted  on  a  common  shaft  and  driving  a  common 
register. 

When  properly  connected,  these  meters  indicate  the  true  power 
in  a  2-phase  3-wire  or  4-wire,  or  a  3-phase  3-wire  circuit,  regard- 
less of  the  power  factor  or  the  degree  of  unbalance  between 
phases. 


FIG.  116. — Westinghouse  single-phase       FIG.     117. — Westinghouse      recording 
watthour-meter — cover  removed.  demand  watthour-meter. 

Extra  terminals  are  provided  on  the  front  of  the  meter  under 
the  cover  to  facilitate  checking  the  meter  while  in  service.  These 
terminals  are  so  arranged  and  connected  by  test-links  that  the 
test  meter  can  be  inserted  in  the  circuit  from  the  front  of  the 
switchboard,  for  testing  the  switchboard  meter,  without  opening 
the  current  transformer  circuits.  By  these  terminals  and  links, 
the  switchboard-meter  elements  can  likewise  be  disconnected 
from  the  transformer  circuits,  the  current  transformers  being 
short-circuited,  and  connected  to  a  test  load  and  portable  stand- 
ard watt-hour  meter. 

Demand  Meter. — The  type  RA  recording  demand  watt-hour 
meter  shown  in  Fig.  117  in  one  unit  measures  both  the  kilowatt 
hours  consumed  and  the  integrated  demand.  It  indicates  on 


186        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


a  four-counter  dial  the  total  kilowatt  hours  consumed  and  records 
in  a  permanent  form  the  integrated  demand  over  successive 
predetermined  time  intervals. 

It  is  applicable  for  determining  the  demand  of  power  installa- 
tions where  a  permanent  record  of  the  demand,  involving  the 
time  and  length  of  occurrences,  is  wanted. 

The  type  RA  recording  demand  watt-hour  meter  consists  of  a 
watt-hour  meter  with  the  usual  four-counter  register  and,  in 
addition,  the  mechanism  for  obtaining  a  graphic  record  of  the 
demand.  The  time  interval  of  the  meter  and  the  advance  of  the 
record  paper  are  controlled  by  a  hand-wound  clock  mechanism. 
Under  load,  the  gear  train  of  the  watt-hour  meter  advances  the 
counters  in  the  regular  manner.  At  the  same  time  the  gear 
train  causes  the  ink-carrying  pen  to  advance  across  the  record 
paper  in  proportion  to  the  energy  registered.  At  the  end  of  a 
predetermined  time  interval  a  stud  on  the  reset  wheel  releases 
the  pen  gear  from  mesh  with  the  gear  train  and  a  balancing  weight 
returns  the  pen  to  zero  where  it  is  again  meshed  with  the  gear 
train  to  repeat  its  advance  during  the  next  time  interval. 

Just  before  the  pen  gear  is  released,  the  record  paper  is  ad- 
vanced a  sixteenth  inch  by  the  operating  spring  so  that  the  pen 
makes  a  distinct  and  readily  observed  record  of  the  maximum  pen 
travel,  showing  both  the  amount  of  integrated  demand  and,  by 

( the    time  calibration  printed  on  the 

record    paper,    the    time    of   its    oc- 
currence. 

The  reset  wheel,  which  makes  one 
complete  revolution  per  hour,  is  ar- 
ranged for  the  insertion  of  four  studs. 
When  all  four  studs  are  used,  the 
meter  has  a  15-minute  time  interval 
on  the  integrated  demand.  With 
two  studs  in  place,  arranged  180  de- 
grees apart,  the  meter  has  a  30- 
minute  time  interval;  and  with  only 
one  stud,  a  60-minute  interval. 

Graphic     Meters. — The   type    M 

Switchboard  graphic  instruments  for  alternating  and  direct- 
current  circuits  shown  in  Fig.  118  make  an  accurate  and 
permanent  record  of  the  electrical  quantities  involved  in  power 
house  operation.  Records  of  kilowatt  output  are  especially 


FIG.     118. — Westinghoust 
graphic  recording  instruments. 


SWITCHBOARD  METERS  187 

important.  The  load  wave  indicated  by  this  instrument  fur- 
nishes a  basis  for  rates  to  prospective  customers  whose  probable 
demands  for  electric  power  during  different  hours  of  the  day 
can  be  estimated. 

Relay  Principle. — All  instruments  operate  on  the  relay  princi- 
ple, the  measuring  element  actuating  only  contacts  and  not  mov- 
ing the  pen  directly.  In  turn,  these  contacts  energize  a  device 
arranged  to  move  the  pen.  The  use  of  resistances  prevents 
harmful  sparking  at  the  contacts,  which  are  made  of  special 
alloy. 

The  approximate  dimensions  of  all  except  direct-current  watt- 
meters are:  over-all  width  13^  inches,  over-all  length  16^  inches, 
over-all  depth  Q/^Q  inches. 

The  record  is  made  by  a  pen  moving  in  a  straight  horizontal  line 
at  right  angles  to  the  motion  of  the  paper,  giving  a  scale  having 
rectangular  co-ordinates. 

The  motion  of  the  pen  and  consequently  the  sensitiveness  of 
the  instrument  may  be  regulated  easily,  and  the  record  made 
either  to  show  slight  variations  in  the  circuit  or  to  slur  over  these 
irregularities  and  form  a  more  even  line.  The  pen  can  be  made 
to  travel  full  scale  in  any  time  from  1  to  30  seconds.  This  motion 
is  absolutely  dead  beat  so  that  the  pen  will  not  "overshoot." 

Paper. — The  record  paper  is  supplied  in  a  long  roll  providing 
continuous  records  for  any  desired  period.  It  is  legibly  printed 
in  black  and  is  inexpensive.  The  width  is  approximately  6% 
inches,  the  scale  being  5^  inches.  Standard  rolls  are  for  two 
month's  service  at  a  speed  of  2  inches  per  hour.  The  standard 
paper  speeds  are  1,  2,  4,  or  8  inches  per  hour.  Each  instrument 
has  a  paper  collecting  roll  of  124  feet  capacity. 

The  clock,  which  turns  the  paper  rolls,  is  of  the  electric  self- 
winding type  and  operates  from  the  control  circuit  at  the  end  of 
each  2-inch  period. 

Paper  Speed. — If  an  instrument  is  desired  the  speed  of  which 
can  be  adjusted  from  8  to  4  or  2  inches  per  hour,  a  clock  suitable 
for  this  purpose  can  be  provided  with  extra  sets  of  gears. 

In  direct-current  ammeters  and  wattmeters  and  in  power 
factor  meters,  the  pen  is  operated  by  solenoids  energized 
through  the  relay  contacts.  In  alternating  current-direct- 
current  voltmeters,  -alternating-current  ammeters  and  watt- 
meters, and  frequency  meters,  the  pen  is  operated  by  a  small 
motor  similarly  energized  through  the  relay  contacts. 


188        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Ammeters,  voltmeters,  wattmeters,  and  frequency  meters  are 
guaranteed  correct  within  1  percent  of  full  scale  at  all  points. 

Meter  Elements. — The  measuring  elements  of  alternating- 
current  and  direct-current  voltmeters,  alternating-current  am- 
meters and  alternating-current  and  direct-current  wattmeters 
are  of  the  Kelvin-balance  type.  They  are  independent  of 
variations  in  frequency,  external  fields,  temperature,  power 
factor,  or  wave  form.  Polyphase  wattmeters  are  correct  with 
any  degree  of  unbalancing  of  phases.  Direct-current  ammeters 
are  of  the  permanent  magnet  type  with  moving  coils,  and  operate 
from  shunts. 

Direct-current  wattmeters  are  similar  to  the  alternating- 
current  wattmeters  except  that  the  series  coils  are  designed  to 
carry  the  total  current. 

Totalizing  Graphic. — Type  M  totalizing  graphic  wattmeter 
is  used  far  measuring  the  total  power  in  a  group  of  2  to  12 
independent  circuits. 

It  is  possible  to  record  on  this  instrument  the  total  power  in 
several  circuits  not  in  synchronism  or  of  different  characteristics 
such  as  frequency,  transformer  ratio,  voltage,  etc.  These  instru- 
ments can  be  made  for  any  capacity  and  frequency  and  can  be 
used  with  instrument  transformers  in  service,  even  though 
of  different  ratios.  The  measuring  elements  are  all  mechanically 
connected  to  one  set  of  contacts,  so  that  it  is  the  total  pull  of  all 
the  elements  that  closes  and  opens  the  contacts.  The  control 
element  is  supplied  for  operation  by  either  direct  current  or  by 
alternating  current,  as  ordered. 

Type  U  Graphics. — These  graphic  ammeters  and  voltmeters 
are  intended  for  purposes  where  graphic  instruments  that  are 
easily  operated,  light  in  weight,  comparatively  low  in  price,  and 
reasonably  accurate  are  required.  The  instrument  consists  of  a 
solenoid  and  core  acting  on  an  arm  that  carries  the  recording 
pen,  and  a  continuous  strip  of  paper  moved  uniformly  by  a  clock 
mechanism.  To  overcome  the  slight  friction  of  the  pen  on  the 
paper,  the  solenoid  is  made  powerful  in  its  action.  Its  action 
is  controlled  by  a  heavy  spring,  which  minimizes  inaccuracies  due 
to  slight  errors  in  leveling.  The  energy  consumed  by  the  volt- 
meter, including  its  external  resistor,  is  25  watts.  The  energy 
consumed  by  the  ammeter  is  7  watts,  thus  adapting  it  for  use 
with  ordinary  current  transformer  for  currents  higher  than  the 
current  rating  of  the  instrument.  On  direct  current  the  type 


SWITCHBOARD  METERS 


189 


U  voltmeters  have  an  accuracy  of  2  percent  and  ammeters  3 
percent,  with  somewhat  greater  accuracy  on  alternating  current. 
Temperature  errors,  and  errors  due  to  ordinary  frequency  changes 
are  negligible. 

Temperature  Indicators. — These  devices  for  switchboard 
mounting  are  desirable,  especially  in  large  capacity  generators, 
in  order  to  know  what  are  the  maximum  temperatures  in  the 
machine  so  that  the  load  may  be  controlled  in  accordance  with 
the  safe  temperature  limits  of  the  insulation. 

Methods. — Three  general  methods  of  temperature  measure- 
ments may  be  used:  by  thermometer,  by  measuring  increase 
in  the  resistance  of  the  windings,  and  by  embedded  temperature 
detectors.  With  the  first  of  these,  surface  temperatures  of 
stationary  parts  only  can  be  observed.  The  second  method 
gives  only  average  temperatures  of  the  winding  and  does  not 
give  temperatures  of  hot  spots.  It  is,  therefore,  upon  the  third 
named  method  that  the  greatest  dependence  can  be  placed. 

There  are  two  forms  of  embedded  detectors  for  temperature 
measurement:  exploring  coils,  and  thermocouples. 

Exploring  Coils. — Outfits  for  use  with  embedded  exploring 
coils  give  a  direct  and  continuous  indication  of  temperature.  A 
separate  source  of  direct  &  ^  Co// 

current  of  constant  voltage 
must  be  provided. 

The  Wheatstone  bridge 
principle  is  used.  The 
exploring  coil  is  a  resistor, 
the  resistance  of  which 
varies  with  the  temperature 
of  the  mass  surrounding  it, 
and  forms  the  fourth  arm 
of  the  bridge.  The  values  of  the  other  three  resistances  of  the 
bridge  are  such  that  when  the  temperature  of  the  exploring  coil 
has  reached  some  predetermined  value  the  bridge  is  in  balance  and 
there  is  no  difference  in  voltage  between  points  2  and  4,  Fig.  119. 
With  the  exploring  coil  at  any  other  temperature,  there  will  be 
a  difference  in  voltage  indicated  on  the  voltmeter  which  is 
calibrated  in  degrees.  The  four  arms  of  the  bridge  are  made 
equal  at  the  temperature  for  which  greatest  accuracy  is  desired, 
and  at  this  temperature  the  indications  will  be  independent  of 
applied  control-circuit  voltage.  The  standard  temperature 


3eries~Re$istor  used  only 
for  Voltages  above  20. 

FIG.   119. — Temperature  indicating  diagram. 


190        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

is  100  degrees  Centigrade,  but  any  other  temperature  may  be 
chosen  for  balance.  The  instrument  can  be  calibrated  for  any 
temperature  that  the  exploring  coils  can  withstand. 

The  exploring  coil  is  made  up  of  a  large  number  of  turns  of 
copper  wire  wound  on  a  strip  of  mica.  The  finished  coil  is 
about  5  inches  long  and  y±  Q  inch  thick  and  at  normal  tempera- 
ture has  a  resistance  of  approximately  30  ohms. 

The  bridge  resistors  are  generally  mounted  in  a  bridge  box 
back  of  the  switchboard  panel,  and  any  source  of  direct  current 
of  constant  voltage  will  serve. 

Thermocouples. — Outfits  for  use  with  embedded  thermo- 
couples balance  the  E.M.F.  of  the  test  couple  against  that  of 
another  couple  at  known  temperature;  it  thus  avoids  all  errors 
due  to  variation  in  leads,  etc.,  and  as  it  indicates  on  the  "null" 
or  zero-reading  principle,  very  accurate  readings  can  be  obtained. 
Danger  of  short  circuit  or  open  circuit  when  placed  in  machine 
is  a  minimum. 

One  thermocouple  is  embedded  in  the  mass  of  which  the 
temperature  is  to  be  measured  and  the  other,  the  "cold"  couple, 
located  where  its  temperature  can  be  easily  recorded  on  a  thermo- 
meter. An  instrument  can  then  be  so  connected  that  it  will 
show  the  difference  in  voltage  between  the  two  couples  and 
therefore  the  temperature  can  be  easily  determined. 

Calibrations. — The  instrument  is  calibrated  to  read  directly 
the  temperature  of  the  test  couple  that  is  made  by  welding  copper 
and  "advance"  (nickel-copper)  alloy  ribbons  together.  These 
ribbons  are  ordinarily  0.005  inch  thick,  0.25  inch  wide  and  of  any 
desired  length.  The  couple  is  insulated  with  mica  and  micarta 
paper  to  withstand  a  temperature  of  at  least  150  degrees  Centi- 
grade. An  inherent  characteristic  of  this  couple  is  that  its 
difference  in  potential  is  42  microvolts  per  degree  Centigrade 
difference  between  the  two  couples. 

The  Westinghouse  type  DT  temperature  indicator  combines 
in  one  case  all  necessary  parts  except  the  test  couple.  It  operates 
on  the  "potentiometer  principle."  The  instrument  case  con- 
tains the  "cold"  couple  which  is  in  contact  with  the  bulb  of  a 
mercury  thermometer,  by  which  the  temperature  of  the  "cold" 
couple  is  observed. 

A  dry  cell  supplies  current  to  a  resistance  wire  equipped  with 
two  sliding  contacts.  The  drop  of  potential  between  these  con- 
tacts is  proportional  to  the  current  in  the  wire  and  to  the  distance 


SWITCHBOARD  METERS  191 

between  them.  Two  pointers  which  move  with  the  contacts 
indicate  the  positions  of  the  two  contacts.  The  scale  is  calib- 
rated in  millivolts  and  degrees;  divisions  on  the  millivolt  scale 
are  of  equal  width;  divisions  on  the  temperature  scale  are  spaced 
according  to  the  E.M.F.  law  of  the  couple.  A  rheostat  in  the 
battery  circuit  is  used  for  adjusting  the  current  exactly  to  the 
value  that  will  cause  a  drop  of  E.M.F.  per  degree  on  the  tempera- 
ture scale  equal  to  the  thermo  E.M.F.  per  degree  in  the  couples. 
Leads  from  the  thermocouple  connect  through  a  sensitive  galva- 
nometer to  the  slide  wire  contacts  of  corresponding  polarity. 
If  the  E.M.F.  between  the  contacts  is  equal  to  the  thermo 
E.M.F.,  there  will  be  no  deflection  of  the  galvanometer.  If 
higher  or  lower,  there  will  be  a  deflection  of  the  galvanometer 
in  one  or  the  other  direction.  By  changing  the  distance  be- 
tween contacts,  using  the  galvanometer  as  a  guide,  the  posi- 
tion at  which  the  slide  E.M.F.  balances  the  thermo  E.M.F. 
is  easily  located. 

In  practice,  the  lower  pointer  is  set  at  the  position  on  the 
scale  corresponding  with  the  temperature  of  the  "cold"  couple 
and  the  upper  pointer  is  moved  until  a  balance  is  obtained  as 
described.  Actual  temperature  of  "hot"  couple  can  then  be  read 
directly  on  the  scale. 

One  galvanometer  serves  both  for  measuring  the  current 
in  the  slide  wire,  in  which  case  it  is  connected  in  multiple  with 
a  shunt,  and  for  indicating  balance  when  it  is  connected  directly 
in  series  with  the  couple. 

Leads. — In  ordinary  practice,  individual  copper  wire  leads  are 
used  to  connect  each  individual  couple  through  a  dial  switch  on 
the  switchboard  to  the  instrument  and  a  common  advance  alloy 
lead  connects  all  the  couples  to  the  instrument.  This  side  of  the 
circuit  is  usually  grounded  in  order  that  no  voltage  may  be 
carried  to  the  switchboard  by  failure  of  the  armature  coil  insula- 
tion to  the  couple,  which  would  allow  generator  potential  on 
the  circuit;  also  in  order  that  any  static  disturbance  may  not 
affect  the  accuracy  of  the  instrument. 

It  is  usual  to  install  six  thermocouples  in  each  generator. 
The  leads  from  these  are  then  brought  out  to  a  terminal  board 
on  the  generator  and  from  there  to  the  switchboard.  By  install- 
ing a  dial  switch  on  the  switchboard,  connection  can  be  made 
readily  from  the  instrument  to  any  one  of  the  couples. 


192        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


WESTON  INSTRUMENTS 

The  Weston  Electrical  Instrument  Company  makes  a  very 
complete  line  of  instruments  for  switchboard  service  as  well  as 
for  laboratory  and  general  testing  purposes. 

Types. — For  D.C.  service,  ammeters  and  voltmeters  are  avail- 
able in  either  round  cases,  illuminated  dial  fan-shaped  cases  or 
vertical  edgewise  cases,  to  suit  different  conditions.  The  higher 
grade  instruments  are  all  made  of  the  pivoted  movable  coil 
permanent  magnet  type  usually  known  as  the  "D'Arsonval" 

type,  with  the  ammeters 
operated  from  shunts  with  a 
drop  of  50  millivolts. 

Round  Pattern.  — The 
round  pattern  meters  are 
made  with  binding  posts  on 
the  front  of  the  meter  or  with 
rear  connected  studs  or  of 
the  flush  type,  the  latter  being 
shown  in  Fig.  120.  The  am- 
meters up  to  75  amperes  are 
self-contained  with  the  shunt 
forming  an  integral  part  of 
the  meter.  For  higher  ca- 
pacities the  shunt  is  separate. 
The  current  at  full  scale  is 

about  0.04  amperes  at  0.05  volts  so  that  the  energy  taken  by 
the  meter  is  only  0.002  watts.  Based  on  a  full  load  of  1000 
amperes  the  loss  in  the  shunt  with  0.05  volts  drop  is  50  watts 
with  proportionate  losses  at  other  currents.  The  round  pattern 
meters,  model  57,  have  an  external  diameter  of  9.562  inches,  a 
scale  length  of  6^  inches.  A  smaller  type  of  round  pattern 
meter  known  as  the  model  24  has  an  external  diameter  of  734 
inches,  a  scale  length  of  5Ke  inches  and  has  an  accuracy  of  1 
percent. 

Eclipse  Meters. — A  cheaper  line  of  round  meters  known  as  the 
"Eclipse"  are  made  on  the  soft-iron  or  electromagnetic  principle. 
The  ammeters  are  connected  directly  in  the  circuit  and  are  built 
in  capacities  up  to  500  amperes.  These  meters  are  made  in  two 
diameters,  the  same  as  for  the  previous  types. 

Illuminated  Dial. — For  large  D.C.  switchboards  illuminated 
dial  meters  can  be  supplied  either  for  attaching  by  means  of 


FIG.  120. — Flush  mounting  round  pattern 
Weston  D.C.  meter. 


SWITCHBOARD  METERS 


193 


brackets  to  the  front  of  the  switchboard  or  of  the  flush  type 
countersunk  in  the  switchboard.  The  scale  length  of  these  meters 
is  11.8  inches  and  the  scale  of  translucent  glass  is  illuminated 
from  the  rear.  The  voltmeters  can  be  supplied  as  differential 
meters  for  paralleling  purposes  or  with  zero  center  where  desired. 
These  meters  have  a  width  of  14.62  inches  and  height  of  13.20 
inches  for  the  normal  type,  but  a  smaller  design  is  available, 
91^e  inches  wide,  8%  inches  high.  For  special  service  instru- 
ments are  available  with  a  scale  length  of  28.09  inches,  width 
27.375  inches,  height  19.50  inches,  or 
with  a  scale  length  of  37.65  inches,  a 
width  of  38.75  inches  and  a  height  of 
29.25  inches. 

Edgewise. — Where  it  is  desired  to 
place  instruments  in  an  elevated  posi- 
tion or  very  close  together,  the  vertical 
edgewise  meters  shown  in  Fig.  121  can 
be  furnished  for  assembling  in  carrying 
frames  accommodating  from  2  to  6  me- 
ters. These  meters  are  so  arranged  that 
they  can  be  tilted  forward  at  any  angle. 

A.C.  Meters. — A  complete  line  of 
A.C.  switchboard  instruments  is  also 
built  by  the  Weston  Company.  For 
ammeters  and  voltmeters  the  soft-iron 
or  electromagnetic  construction  is  FIG.  121 . — Vertical  edgewise 

i       ,     i  i    ,1  j          f  Weston  meter. 

adopted  and  the   meters  are   made    of 

the  round  type  either  9%  inches  or  7K  inches  diameter  and 

have  scales  that  are  fairly  uniform. 

Wattmeters. — The  wattmeters  are  built  on  the  electrodyna- 
mometer  principle,  as  are  the  synchronoscope  and  power  factor 
meter.  The  fixed  winding  of  a  single-phase  wattmeter  is  made  up 
of  two  coils  which  act  together  to  produce  the  field  of  the  watt- 
meter, these  being  fed  from  a  series  transformer.  The  movable 
coil  placed  inside  the  fixed  coils  is  connected  in  series  with  a 
resistor  in  a  voltage  circuit.  The  general  appearance  of  a 
single-phase  wattmeter  is  shown  in  Fig.  122.  As  the  current 
in  the  series  (stationary)  coils  increases  the  movable  (potential) 
coil  tends  to  turn  so  that  the  fields  of  the  two  elements  will 
coincide.  This  tendency  is  resisted  by  a  spring  but  the  movable 
coil  in  turning  causes  the  pointer  to  pass  over  the  scale  until  a 


194        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


FIG.  122. — Weston  indicating  wattmeter. 


point  is  reached  when  the  torque  of  the  coils  is  just  equal  to  the 
restraining  torque  of  the  spring.  The  polyphase  wattmeter  has 
two  of  the  single-phase  meter  elements  so  located  in  tandem  as  to 
act  on  the  same  shaft. 

The  field  coils  of  the  synchronoscope  are  very  similar  to  those 
of  the  wattmeter,  except  that  they  are  wound  with  much  smaller 

wire  as  they  are  essentially 
potential  coils  in  place  of 
current  coils.  The  field  coils 
of  the  power  factor  meter 
are  similarly  placed  but  made 
in  an  elongated  form. 

In  all  of  these  instruments 
the  pointer  is  made  in  the 
form  of  a  triangular  truss 
with  tubular  members,  mak- 
ing a  very  stiff  construction 
with  very  small  weight.  An 
effective  form  of  air  damper 
is  used,  made  with  very  thin 
metal  stiffened  with  ribs,  the 
whole  damper  being  placed  in  a  damper  box  where  the  air  leakage 
is  reduced  to  a  minimum,  increasing  greatly  the  amount  of  damping 
while  keeping  down  the  weight  and  the  moment  of  inertia. 

Synchronoscope. — The  Weston  synchronoscope  has  a  switch- 
board electrodynamometer  movement,  mounted  with  the 
pointer  behind  a  translucent  glass  scale  and  illuminated  by  a 
synchronizing  lamp  connected  to  synchronize  light.  The  fixed 
coil  is  connected  across  the  line  through  a  resistor  and  the  mov- 
able coil  is  connected  through  a  condenser  across  the  incoming 
machine.  The  pointer  stands  normally  in  the  middle  of  the 
scale.  The  mechanical  construction  of  this  instrument  is  similar 
to  that  of  the  Weston  single-phase  wattmeter,  except  that  both 
the  fixed  and  movable  coils  are  wound  with  fine  wire. 

Since  the  lamp  is  dark  when  the  E.  M. Fs.  are  in  phase  opposition, 
and  light  when  they  are  in  phase  coincidence  and  have  the  same 
frequency,  the  pointer  will  be  seen  at  rest  in  the  middle  of  the 
scale  when  perfect  synchronism  is  attained. 

When  the  E.M.Fs.  are  not  exactly  in  phase  or  in  phase  opposi- 
tion, there  will  be  torque  tending  to  turn  the  movable  coil,  the 
value  of  the  torque  increasing  with  the  phase  displacement. 


SWITCHBOARD  METERS 


195 


The  direction  of  the  torque  depends  upon  the  relative  directions 
of  the  currents  in  the  coils;  that  is,  the  direction  of  deflection  in- 
dicates whether  one  lags  or  leads  with  respect  to  the  other. 
If  the  two  machines  are  not  running  at  the  same  frequency,  the 
phase  displacement  will  continuously  shift  from  phase  coincidence 
through  complete  cylces  of  360  time-degrees,  and  with  it  the 
torque  will  vary  continuously  from  zero  to  plus  maximum,  back 
through  zero  to  minus  maximum,  etc.,  thus  causing  the  pointer 
to  swing  back  and  forth  over  the  scale.  Each  swing  denotes  a 
shift  in  phase  angle  from  quadrature  plus  or  minus  to  quadra- 
ture minus  or  plus,  and,  therefore,  it  will  coincide  with  a  period  of 
light  or  darkness,  and  the  pointer  will  be  seen  only  during  every 
other  swing;  that  is,  it  will  appear  to  rotate  in  one  direction. 


FIG.  123. — Diagram  of  connections.     Weston  synchronoscope. 

The  direction  of  apparent  rotation  indicates  whether  the  incom- 
ing machine  is  fast  or  slow  and  the  speed  of  rotation  is  a  measure 
of  the  amount  by  which  the  frequencies  differ.  If  the  machines 
have  the  same  frequency  but  are  not  in  phase  coincidence,  the 
pointer  will  come  to  rest  at  some  point  at  one  side  or  the  other  of 
the  middle  of  the  scale. 

The  connections  of  the  various  operating  parts  of  the  synchro- 
noscope are  shown  schematically  in  Fig.  123. 

Power  Factor  Meter. — The  powerfactor  meter  is  a  special 
form  of  electrodynamometer.  Its  movable  system  consists  of 
two  circular  coils  arranged  on  the  same  staff  and  in  planes 
at  right  angles  to  each  other.  The  movable  coils  of  the  power 
factor  meter  are  practically  identical  in  magnetic  strength 


196        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

when  traversed  by  the  same  current,  and  are  accurately  and 
permanently  located  in  planes  at  right  angles  to  each  other. 
The  coils  are  wound  by  machine  and  interlaced  layer  for  layer 
at  diametral  crossing  points.  The  completed  coil  is  then  treated 
with  a  special  cement  which  gives  it  exceedingly  great  rigidity, 
and  thus  assures  a  permanent  relative  location  of  the  coils. 
The  general  construction  is  quite  similar  to  that  of  the  single 
phase  wattmeter. 

On  polyphase  systems,  the  movable  coils  are  connected  across 
leads  in  which  the  E.M.F.  differs  in  time-phase,  while  on  single- 
phase  circuits  a  phase-splitting  device  is  used.  When  the  current 
in  one  of  the  movable  coils  is  in  time-phase  with  that  in  the  fixed 
coil  it  will  place  itself  parallel  with  the  fixed  coil.  If  the  current 
in  the  fixed  coil  reaches  its  maximum  at  some  time  intermediate 
between  the  time  of  maximum  current  in  either  of  the  other  coils, 
the  movable  coils  will  take  a  position  such  that  the  resultant 
maximum  field,  which  is  in  time-phase  with  the  fixed  field,  due 
to  the  fixed  coil  will  coincide  with  the  fixed  field. 

Since  the  fixed  field  is  in  time-phase  with  the  load  current,  and 
the  field  of  one  of  the  movable  coils  is  in  time-phase  with  the 
E.M.F.  between  leads,  the  space  position  of  the  resultant  field  of 
the  movable  coils,  which  is  in  phase  with  the  fixed  field,  will  vary 
with  the  phase  angle  between  E.M.F.  and  current;  that  is,  the 
deflection  of  the  movable  system  is  a  measure  of  phase  angle  or 
power  factor. 

Frequency  Meter. — This  meter  indicates  accurately  the  in- 
stantaneous value  of  the  frequency  of  the  system  to  which  it 
is  connected.  Its  movement  is  of  the  soft-iron  type  with  two 
fixed  coils,  each  made  up  of  two  sections.  They  are  wound 
flat  and  one  is  slipped  inside  the  other  and  at  right  angles  to  it. 
The  movable  system  consists  of  a  staff  carrying  a  damper,  an  iron 
needle  and  a  pointer;  it  is  mounted  in  highly  polished  sapphire 
jewel  bearings.  There  are  no  springs  or  other  connections  to  the 
movable  system,  therefore,  it  is  perfectly  free  to  rotate. 

The  shape  of  the  fixed  coil  is  such  as  to  establish  with  minimum 
material  a  strong  field  of  uniform  density,  such  as  is  necessary  to 
the  production  of  uniform  scale.  The  needle  is  extremely  thin 
and  is  made  of  a  special  alloy  having  a  low  hysteretic  constant. 

The  coils  are  connected  in  series  across  the  line,  with  a  reactor 
in  series  with  one  and  a  resistor  in  series  with  the  other.  A  re- 
sistor is  connected  in  parallel  with  one  coil  and  the  reactor,  and 


SWITCHBOARD  METERS  197 

a  reactor  is  connected  in  parallel  with  the  other  coil  and  the  re- 
sistor; then  the  whole  combination  is  connected  in  series  with  a 
reactor,  the  purpose  of  which  is  to  damp  out  the  higher  harmonics. 
The  circuits  form  a  Wheatstone  bridge,  which  is  balanced  at 
normal  frequency.  An  increase  in  frequency  will  increase  the 
reactance  of  the  reactors  and  thus  upset  the  balance  of  the  bridge, 
allowing  more  current  through  one  coil  and  less  through  the  other. 
Therefore,  every  change  in  frequency  is  accompanied  by  a  cor- 
responding shifting  of  the  space  position  of  the  resultant  field, 
which  is  indicated  by  the  pointer. 

These  A.C.  meters  are  usually  made  about  9%  inches  in 
diameter  but  the  ammeters  and  voltmeters  can  also  be  furnished 
73^  inch  diameter. 


CHAPTER  VII 
INSTRUMENT  TRANSFORMERS 

Functions. — Owing  to  the  small  amount  of  power  required  for 
the  operation  of  A.C.  switchboard  instruments,  circuit-breaker 
trip  coils  and  relays,  and  the  difficulty  of  insulating  them  for 
high  voltages  or  making  them  with  current  coils  of  large  capacity, 
it  is  customary  to  furnish  voltage  transformers  for  pressures 
over  600  volts  and  to  use  current  transformers  where  the  current 
exceeds  a  certain  value  or  the  voltage  is  above  2400  volts.  For 
the  purpose  of  interchangeability  most  instruments  and  relays 
used  with  transformers  are  made  with  voltage  coils  to  be  operated 
at  a  maximum  of  150  volts  and  current  coils  for  a  maximum  of  5 
amperes. 

Voltage. — The  voltage  transformers  are  made  of  the  dry  type 
for  pressures  of  200  to  6000  volts,  while  oil  insulated  voltage 
transformers  are  made  for  pressures  of  200  to  60,000  volts  or 
higher.  Where  these  voltage  transformers  are  used  with  from 
one  to  three  instruments  they  are  usually  compensated  to  give 
accurate  transformation  ratios  at  an  output  of  15  volt  amperes, 
while  with  a  greater  number  of  instruments  or  when  used  with  a 
regulator  or  similar  device  they  are  compensated  to  give  a  correct 
ratio  at  100  or  200-volt  ampere  outputs. 

Currents. — Current  transformers  are  made  in  various  designs, 
either  dry  or  oil  immersed,  depending  on  the  voltage.  As  a 
rule  the  current  transformer  steps  down  from  a  comparatively 
large  current  to  a  smaller  one  and  the  primary  consists  of  a  few 
turns  connected  directly  in  the  main  circuit.  For  very  accurate 
work  the  number  of  ampere-turns  should  be  at  least  600  but 
where  great  accuracy  is  not  required  and  the  secondary  load  is 
small  the  number  of  primary  ampere-turns  can  be  greatly  reduced. 
For  currents  of  600  amperes  or  more,  transformers  with  accurate 
current  ratio  and  very  small  "phase  displacement  error"  can 
be  made  without  any  primary  winding  and  arranged  to  slip  over 
the  cable,  switch  stud,  bus  bar  strap  or  similar  connection,  which 
then  forms  the  primary.  For  use  with  relays  or  with  ammeters 

198 


INSTRUMENT   TRANSFORMERS  199 

calibrated  specially  current  transformers  of  this  type  can  be 
made  for  ratios  down  to  100-5,  or  even  smaller  in  certain  cases. 

Oil  Immersed. — For  high  voltage  service  oil  immersed  current 
transformers  are  used  and  where  it  is  desirable  to  have  two  differ- 
ent current  ratios  for  the  operation  of  various  instruments  and 
relays  it  is  possible  to  build  transformers  with  one  primary  coil, 
two  iron  circuits  and  two  secondary  coils  to  give  the  two  different 
ratios  desired.  Dry  type  transformers  are  also  built  of  this 
"double  secondary"  construction. 

By  the  use  of  current  and  potential  transformers  low  voltage 
circuits  are  obtained  with  characteristics  in  practical  agreement 
with  the  high  voltage  circuit.  Current  transformers  are  ex- 
tensively used  to  obviate  the  necessity  of  carrying  large  or  high 
voltage  conductors  to  instruments  and  protective  devices. 

Purpose. — An  instrument  transformer  is  a  device  suitable  for 
use  with  measuring  instruments  in  which  the  conditions  of  cur- 
rent, potential  and  phase  in  the  primary  or  high  voltage  circuit 
are  represented  with  acceptable  accuracy  in  the  secondary  or  low 
voltage  circuit. 

While  accuracy  is  of  vital  importance,  it  is  absolutely  essential 
in  current  transformers  that  their  construction  be  such  as  to 
withstand  momentarily  short-circuit  currents  many  times  their 
rated  carrying  capacity  without  injury.  Furthermore,  it  is  of 
great  importance  that  the  design  afford  a  high  degree  of  insula- 
tion. Unusual  care  has  been  exercised  in  the  design  of  trans- 
formers to  provide  a  high  factor  of  safety. 

Load. — Tripping  coils  of  most  protective  devices  usually 
impose  a  heavy  "burden"  upon  current  transformers.  Where 
extreme  accuracy  is  required,  it  is  recommended  that  separate 
instrument  transformers  be  used  to  supply  energy  to  instruments 
or  meters,  and  that  tripping  transformers  be  used  in  connection 
with  trip  coils  of  protective  devices. 

Precautions. — Current  transformers  should  not  be  mounted 
where  they  will  be  exposed  to  unduly  high  temperatures,  oil 
drippings,  moisture,  etc.,  and  care  should  be  taken  that  the 
primary  terminals  are  properly  insulated. 

In  mounting  current  and  potential  transformers,  sufficient 
distance  should  be  provided  between  terminals  of  adjacent  trans- 
formers and  between  terminal  and  ground,  to  prevent  flash-over 
due  to  momentary  voltage  surges.  The  transformer  frame  and 
secondary  windings  should  be  thoroughly  grounded  to  eliminate 


200        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


electrostatic  charges  and  afford  protection  to  attendants.  Con- 
tact to  ground  should  be  thoroughly  inspected  before  working  on 
the  circuit. 

The  secondary  circuit  of  current  transformers  should  not  be 
opened  with  current  in  the  primary,  owing  to  the  high  voltage 
momentarily  induced  when  the  circuit  is  opened.  It  is  well  al- 
ways to  short-circuit  the  secondary  windings  of  current  trans- 
formers before  disconnecting  instruments,  meters,  or  tripping 
coils. 

Transformers  should  be  handled  with  care  to  prevent  mechani- 
cal injury  or  possible  weakning  of  insulation. 

Makers. — Nearly  all  manufacturers  of  instruments  and  oil 
circuit  breakers  make  current  and  potential  transformers  for  use 
with  them.  Those  of  the  Condit  Company  and  the  Westinghouse 
Company  have  been  selected  for  description  as  being  fairly  typical. 

Types. — The  current  transformers  of  the  Condit  Electric 
Manufacturing  Company,  are  built  in  two  sets  of  types,  the 
*B'  for  circuit-breaker  tripping,  and  the  'S'  intended  for  use 
with  meters  as  well  as  trip  coils. 


FIG.  124. — Condit  Electric  &  Mfg.  Co.  current  transformer  type  B-6. 


Type  B-6. — This  type  shown  in  Fig.  124  is  intended  for  primary 
windings  from  5  to  200  amperes  at  voltages  not  exceeding  7500 
for  either  25  cycles  or  60,  to  carry  a  load  of  one  ammeter  and  one 
indicating  wattmeter  for  the  best  efficiency  and  a  maximum  load 
of  one  ammeter  and  one  circuit-breaker  coil.  It  has  a  capacity 
of  about  50  volt  amperes.  It  is  made  with  a  wound  primary  con- 
taining the  proper  number  of  turns,  and  it  is  designed  to  stand  the 


INSTRUMENT  TRANSFORMERS 


201 


electromagnetic  and  thermal  effects  resulting  from  sustained 
short  circuits. 

Type  B-4.— The  type  B-4,  Fig.  125,  for  currents  from  300 
to  600  amperes  at  voltages  not  exceeding  7500,  is  intended  for 
slipping  over  a  cable  or  stud  and  is  provided  with  a  circular  open- 
ing 2  inches  in  diameter.  It  has  an  output  of  40  volt  amperes 
with  5  amperes  in  the  secondary  at  60  cycles  and  20  at  25  cycles. 


Fio.  125. — Condit  Elec.  &  Mfg.  Co.  current  transformer  type  "B-4." 

Type  B-5. — This  is  made  for  currents  from  600  to  1200  at 
voltages  not  exceeding  4500  and  is  intended  for  slipping  over  rec- 
tangular bars  and  has  an  opening  of  1% Q  x  4^f  6  inches.  It 
has  same  output  as  the  type  B-4  and  same  general  appearance 
except  provided  with  a  rectangular  opening  in  place  of  circular. 

Type  B-8. — This  is  built  for  currents  from  1500  to  3000  and  is 
intended  for  slipping  over  rectangular  bus  bars  or  multiple  cables 
for  voltages  not  exceeding  4500.  It  has  an  output  of  50  volt 
amperes  at  60  cycles  and  25  at  25  cycles.  It  has  an  opening 
2%  x  4^  inches. 

These  larger  capacity  transformers  are  designed  primarily 
for  operating  circuit-breaker  trip  coils,  but  they  may  be  used  to 
operate  indicating  meters  in  conjunction  with  trip  coils  and  will 
afford  the  usual  accuracy  required  of  indicating  meters  for  switch- 
board service. 

Type  B-7. — These  current  transformers  are  built  for  currents 
from  300  to  500  amperes  for  voltages  up  to  15,000  and  are  intend- 
ed to  withstand  heavy  short-circuit  stresses  without  distortion. 
It  has  the  same  output  as  the  B-4.  The  B-9  and  B-ll  trans- 
formers have  current  ratings  from  5  to  300  amperes  for  voltages 
up  to  25,000  and  50,000  volts  respectively  for  indoor  service  and 
the  B-13  and  B-14  are  the  corresponding  outdoor  transformers. 


202        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Type  SI  &  SC. — The  type  SI  current  transformers  are  built 
double  ratio  for  currents  from  5  to  800  amperes  and  voltages  up  to 
15,000  for  circuit-breaker  trip  coils  and  indicating  meters.  It  can 
readily  be  used  as  a  differential  transformer,  and  is  built  to  with- 
stand short-circuit  stresses  on  large  systems.  It  has  an  output 
of  60  volt  amperes  at  60  cycles  and  30  at  25  cycles.  The  type 
SC  is  designed  primarily  for  use  with  instruments  where  a  high 
degree  of  accuracy  is  desired.  It  resembles  the  type  SI  in  its 
general  features. 


FIG.  126. — Condit  Electric  Mfg.  Co.,  potential  transformer,  type  "W.' 


Voltage  Transformer. — The  type  W  transformer,  Fig.  126,  is  dry 
insulated,  thoroughly  impregnated,  and  exceptional  care  has  been 
exercised  to  provide  a  high  factor  of  insulation.  All  transformers 
have  one  primary  and  one  secondary  lead  properly  marked  to 
indicate  the  polarity.  The  windings  are  so  related  that  the  in- 
stantaneous "ingoing  current"  of  the  marked  high  voltage  or 
primary  lead  corresponds  to  the  "outgoing  current"  of  the 
marked  low  voltage  or  secondary  lead.  The  transformer  is  so 
constructed  that  a  minimum  space  is  required  for  its  instal- 
lation. For  pressures  of  2500  volts  or  less,  the  cut-out  base  may 
be  furnished  as  an  integral  part  of  the  transformer  and  makes  a 
very  compact  and  neat  arrangement.  On  pressures  in  excess  of 
2500  volts  the  fuse  base  must  be  separately  mounted.  Oil 
insulated  transformers  are  supplied  for  pressures  in  excess  of 
5500  volts. 

GENERAL  ELECTRIC  TRANSFORMERS 

The  General  Electric  Company  have  a  very  complete  line  of 
current  and  potential  transformers  for  all  classes  of  service  prac- 


INSTRUMENT  TRANSFORMERS 


203 


tically  paralleling  the  line  of  Westinghouse  transformers  whose 
description  follows. 

WESTINGHOUSE  TRANSFORMERS 

Type  K. — Westinghouse  current  transformers,  type  A  (dry 
type)  indoor,  are  designed  for  normal  voltage  of  4600  2- 
wire,  1150  3-wire,  test  voltage  for  one  minute  of  14,000  2-wire, 
5000  3-wire;  for  25  to  133  cycle  circuits;  capacity  25  volt  amperes, 
compensated  for  12^  volt  amperes. 

Two-wire. — The  type  K  2-wire  transformers  comprise  a  line 
of  low  priced  transformers  of  good  accuracy,  available  over  a  large 
range  of  application.  This  type  is  suitable  for  ammeter,  watt- 
meter, or  watt-hour  meter  use,  but  may  be  used  also  for  operating 
relays  and  circuit-breaker  trip  coils  where  the  load  at  4  amperes 
does  not  exceed  25  volt  amperes  at  25  cycles  or  65  volt  amperes 
at  60  cycles.  They  should  not  be  used  with  relays  where  the 
circuit-breaker  trip  coil  is  connected  in  series  with  the  relay. 

Three-wire  Type  K. — Designed  for  use  with  watt-hour  meters 
on  3-wire  distribution  systems.  The  primary  consists  of  two 
separate  windings,  one  of  which  is  connected  in  each  outside  wire 
of  the  3-wire  system,  and  the  secondary  winding  is  connected 
to  the  watt-hour  meter.  When  so  connected,  the  watt-hour 
meter  measures  the  total  output  of  the  system.  The  ampere 
rating  refers  to  the  current  in  the  outside  wires. 


FIG.  127. — Westinghouse  current  transformer  type  "  KA." 

Types  KA  and  KB. — These  dry  type  indoor  transformers  are 
built  for  a  normal  voltage  of  6900  and  13,800,  a  test  voltage 
of  16,500  and  33,000  for  1  minute;  for  25  to  133  cycle  circuits; 
capacity  50  volt  amperes,  compensated  for  25  volt  amperes.  A 


204        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


Hand  Hole 
Cover 


high  degree  of  accuracy  in  the  ratio  of  primary  to  secondary 
current  and  a  minimum  phase  displacement  error  are  obtained 
in  these  transformers.  This  type  is  for  indoor  use  in  all  cases 
where  highest  accuracy  is  required. 

As  shown  in  Fig.  127,  the  transformers  are  arranged  with  the 
primary  leads  on  the  opposite  ends  of  the  coils,  an  arrangement 
well  adapted  for  switchboard  use.  Lugs  are  provided  for 
mounting  purposes. 

Type    KC. — These  dry  type  indoor  transformers  are  built 
for  a  normal  voltage  of  23,000,  test  voltage  of  52,200  for  1 
minute;  for  25  to  133  cycle  circuits;  capacity  50  volt  amperes, 
compensated  for  25  volt  amperes.     They  are  mounted  in  cast- 
iron    end   caps  which  are 
filled  with  insulating  com- 
pound.    This  construction 
insures    ample    insulation 
between  the  high  voltage 
winding  and  the  secondary 
winding  or  the  core. 

Double  secondary  type 
KC  transformers  shown  in 
Fig.  128  are  similar  in  con- 
struction and  voltage 
rating  to  the  type  KC, 
but  have  two  independent 
secondary  windings,  each 
compensated  for  25  volt 
amperes.  One  of  these 

transformers,   therefore,  takes  the  place  of  two  ordinary  trans- 
formers on  the  same  circuit. 

Relay  Transformers. — Type  KR  (dry  type)  indoor  trans- 
formers for  operating  relays  and  circuit-breaker  trip  coils  have  a 
maximum  voltage  of  6900,  test  voltage,  16,500  for  1  minute, 
for  25  to  133  cycle  circuits.  This  line  of  transformers  in  capa- 
cities 5  to  200  amperes  inclusive  is  supplementary,  for  circuit- 
breaker  use,  to  the  through  type  FR  transformers  listed  in 
capacities  up  to  500  amperes.  These  transformers  have  sufficient 
capacity  to  operate  relays  or  trip  coils  and  will  have  an  error  in 
ratio  not  exceeding  about  10  per  cent,  where  the  load  at  4  amperes 
does  not  exceed  25  volt  amperes  at  25  cycles  or  65  volt  amperes  at 


FIG.  128. — Westinghouse  current  transformer 
type  "  KC  "  double  secondary. 


INSTRUMENT  TRANSFORMERS  205 

60  cycles.  They  should  not  be  used  with  relays  where  the  circuit- 
breaker  trip  coil  is  in  series  with  the  relay. 

These  transformers  are  for  use  only  with  relays,  or  circuit- 
breaker  trip  coils.  They  have  sufficient  capacity  for  operating 
circuit  breakers  within  the  limits  of  ordinary  accuracy  demanded 
in  such  service  but  should  not  be  used  for  connection  to  measuring 
instruments.  The  general  type  of  construction  is  similar  to 
type  KA  transformers,  except  that  these  are  much  smaller. 

The  through-type  FR  (dry  type)  indoor  transformers  for 
operating  relays  and  circuit-breaker  trip  coils,  for  25  to  133 
cycle  circuits  are  similar  to  types  FS  and  FB ;  but  in  the  capaci- 
ties covered  by  this  line,  100  to  500  amperes  inclusive,  a  through- 
type  transformer  cannot  be  made  of  sufficient  accuracy  for 
ordinary  use  in  connection  with  measuring  instruments.  This 
line  of  transformers  is,  therefore,  primarily  adapted  for  circuit- 
breaker  tripping,  either  through  relays  or  by  direct  connection 
to  the  breaker. 

Special  Calibration. — In  order  to  obtain  the  advantage  of  a 
through-type  transformer  of  low  current  rating  for  instrument 
service,  these  transformers  may  be  so  used  where  it  is  possible  to 
calibrate  the  instrument  with  the  transformer.  This  application 
can  only  be  made  in  the  case  of  ammeters,  and  requires  the  use  of 
a  calibration  curve  for  each  instrument.  The  same  transformers 
should  not,  however,  be  used  both  for  instrument  work  and 
circuit-breaker  work.  These  transformers  have  sufficient  capa- 
city to  operate  relays  or  trip  coils  and  will  have  an  error  in  ratio 
not  exceeding  about  10  per  cent,  where  the  load  at  4  amperes 
does  not  exceed  exceed  25  volt  amperes  at  25  cycles  or  55  volt 
amperes  at  60  cycles.  They  should  not  be  used  with  relays 
where  the  circuit-breaker  trip  coil  is  in  series  with  the  relay. 

Through-types. — Types  FS  and  FB  (dry  type)  indoor  trans- 
formers have  a  rated  voltage  of  2300,  test  voltage  10,000  for 
1  minute,  for  25  to  133-cycle  circuits.  These  transformers  in 
capacities  up  to  6000  amperes  have  a  potential  rating  of  2300 
volts.  By  the  use  of  longer  insulating  tubes  over  the  primary 
conductor,  they  may  be  used  at  higher  voltages.  In  sizes  up  to 
and  including  1000  amperes,  they  have  a  capacity  of  25  volt 
amperes  and  are  compensated  for  12^  volt  amperes;  above  1000 
amperes  they  have  a  capacity  of  50  volt  amperes  and  are 
compensated  for  25  volt  amperes.  These  "through-type" 
transformers  have  no  primary  windings  but  slip  over  a  cable, 


206       SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


stud,  or  bus  bar,  which  forms  the  primary  of  the  transformer. 
The  type  FS  is  intended  for  cables  and  round  studs,  and  the  type 
FB  for  rectangular  bus  bars. 

Short  Circuits. — The  momentary  current  due  to  a  heavy  short 
circuit  on  a  large  system  is  extremely  great,  and  the  mechanical 
stresses  set  up  between  the  primary  and  secondary  windings  of  a 
current  transformer  due  to  this  current  are  extraordinarily  large. 
The  "through-type"  of  transformer  is  the  only  type  in  which 
these  stresses  are  balanced  up  within  the  transformer  itself; 
and  they  are  therefore  of  special  value  where,  due  to  special 
conditions,  other  types  of  transformers  are  liable  to  overstrain 
from  such  stresses. 

Outdoor  Types.— Types  MA,  MB  or  MC  (dry  type)  outdoor 
transformers  have  rated  voltage  of  6900,  138,000  and  23,000; 
test  voltage  of  16,500,  33,000  or  52,200  for 
1  minute;  for  25  to  133  cycle  circuits;  capacity 
50  volt  amperes,  compensated  for  25  volt 
amperes.  These  transformers  are  mounted 
in  cast-iron  end  caps  with  the  leads  extending 
downwards  through  suitable  bushings.  The 
transformers  are  impregnated  with  an  in- 
sulating compound  which  thoroughly  seals  up 
joints  between  the  laminations  and  end  caps. 
Oil  Insulated.— Types  OA,  OB  or  OC  (oil 
insulated)  transformers  have  a  normal 
voltage  of  34,500,  44,000  or  66,000  and  a  test 
voltage  of  69,000,  88,000  or  132,000  for  1 
minute;  for  25  to  133  cycle  circuits;  capacity 
50  volt  amperes,  compensated  for  25  volt 
amperes.  These  transformers  are  designed 
for  separate  mounting,  in  compartments  or 
otherwise.  They  are  heavily  insulated  between 
primary  and  secondary  windings  and  form  a 
barrier  of  great  strength  between  the  line  and 
the  instrument  circuits. 

Double  Secondary. — In  cases  where  it  is 
desirable  to  operate  relays  or  circuit  breakers 
together  with  indicating  instruments  or  watt-hour  meters,  trans- 
formers having  two  independent  secondary  circuits  can  be  fur- 
nished. The  instruments  can  then  be  isolated  from  the  relays  or 
circuit  breakers,  and  the  accuracy  of  the  former  will  be  unaffected 
by  the  heavy  load  represented  by  the  latter. 


FIG.  129.— West- 
inghouse  outdoor  oil 
immersed  current 
transformer  66  K.V. 


INSTRUMENT  TRANSFORMERS 


207 


Outdoor  transformers  like  Fig.  129  differ  from  the  indoor  type 
only  in  having  high  voltage  outlet  bushings  suitable  for  outdoor 
service. 

Voltage  Transformers. — These  are  made  either  dry  type  or 
oil  insulated.  The  dry  type  voltage  transformers  are  mounted  in 
end  frames  and  are  adapted  for  use  on  voltages  up  to  6000.  The 
end  frames  of  transformers  up  to  and  including  2000  volts  have 
lugs  cast  on  them  for  mounting  fuse  blocks. 

Oil  Insulated  Voltage  Transformers. — The  oil  insulated  type 
voltage  transformers  are  designed  for  use  on  voltages  from  2300 
to  66,000.  Up  to  6900  volts  they  are 
mounted  in  cases  made  to  fit  in  cells 
or  in  the  limited  space  behind  switch- 
boards. For  voltages  up  to  6900,  they 
are  mounted  in  cast-iron  cases  provided 
with  mounting  lugs.  For  voltages 
above  6900,  the  transformers  are  built 
for  floor  mounting.  For  voltages  of 
4000  to  6900  inclusive,  the  trans- 
formers are  so  designed  that  the  high 
voltage  leads  can  be  brought  through 
either  the  top  or  the  sides  of  the  case, 
by  means  of  the  extra  bushing  holes 
and  flanges.  This  feature  is  of  par- 
ticular advantage  in  switchboard 
wiring.  Oil  insulated  transformers  for 
outdoor  operation  like  Fig.  130  can  be 
furnished  for  standard  voltages. 

The  ratio  of  transformation  should  be  such  as  to  give  a  nominal 
voltage  of  100  on  the  instruments.  Thus,  for  a  2200-volt  cir- 
cuit, a  2000-100  ratio  should  be  used,  making  the  normal  voltage 
on  the  instruments  110. 

For  protection  against  line  surges,  transformers  designed  for 
voltages  of  22,000  and  above,  have  choke  coils  mounted  in  their 
cases  and  connected  between  the  transformer  windings  and  the 
line. 

Outdoor  Metering. — These  equipments  as  shown  in  Fig.  131 
are  designed  for  supplying  service  from  high  voltage  transmission 
lines  where  the  expense  of  a  substation  is  not  warranted,  these 
metering  equipments  being  furnished  enclosed  in  weatherproof 
casings.  Each  equipment  consists  of  a  standard  polyphase 


FIG.  130. — Westinghouse 
outdoor  oil  immersed  poten- 
tial transformer  66  KV. 


208        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


watt-hour  meter,  two  current  transformers,  a  polyphase  voltage 
transformer,  and  three  choke  coils  to  protect  the  transformer 
windings  against  high-frequency  disturbances;  all  enclosed  in  a 
sheet  steel  case  with  cast-iron  cover.  The  sheet  steel  case  is 
subdivided  into  2  compartments,  one  of  which  is  filled  with  oil 
in  which  the  transformers  and  choke  coils  are  immersed,  while 


FIG.  131. — Westinghouse  outdoor  metering  equipment. 

the  other  serves  to  enclose  the  meter  and  meter  panel.  On  the 
meter  panel  are  also  mounted  two  fuses  to  protect  the  voltage 
circuit  of  the  meter  and  two  calibrating  links  located  in  the  cur- 
rent circuit  of  the  meter.  The  meter  may  be  read  or  checked 
upon  opening  the  hinged  door  which  covers  the  entire  front  of 
the  meter  compartment.  The  arrangement  is  such  that  the 
entire  outfit,  including  meter  panel,  can  be  raised  out  of  the  tank 
without  disconnecting  the  meter  leads. 


CHAPTER  VIII 
LIGHTNING  ARRESTERS 

The  apparatus  furnished  for  the  protection  of  electrical 
equipment  against  the  effects  of  lightning  or  static  disturbances 
of  any  kind  is  usually  considered  as  part  of  the  switching  devices 
and  is  frequently  included  in  the  same  contract  as  the  switch- 
board and  the  switching  apparatus.  For  this  reason  it  seems 
logical  to  take  up  its  consideration  in  this  book  after  the  circuit 
breakers,  relays,  meters  and  instrument  transformers. 

Terms. — Lightning,  from  the  protective  standpoint,  is  a 
term  used  to  cover  all  kinds  of  disturbances  in  electrical  trans- 
mission systems  that  take  the  form  of  high  voltage.  There 
are  two  kinds  of  lightning,  viz.:  that  due  to  atmospheric  lightning, 
and  that  due  to  internal  disturbances  in  the  line  itself.  Lightning 
arresters  are  designed  to  take  care  of  atmospheric  lightning 
and  those  internal  surges  that  are  transient  in  nature,  but  not 
those  that  are  continuous. 

Cause. — Atmospheric  lightning  is  due  to  discharges  that 
occur  between  two  oppositely  charged  clouds  or  between  a 
cloud  and  the  earth. 

Direct  Strokes. — When  a  discharge  from  a  cloud  strikes  an 
electrical  conductor  directly,  it  almost  always  breaks  down 
the  insulation  at  or  very  near  that  point.  It  rarely  travels 
along  a  transmission  line  far  enough  to  reach  an  arrester  and  if 
it  did  it  would  probably  destroy  any  type  of  arrester  except 
possibly  an  electrolytic  one.  Arresters  are  not  designed,  there- 
fore, to  handle  direct  lightning  strokes.  It  is  usually  the  line 
insulators  rather  than  the  station  apparatus  that  are  injured  by 
these  direct  strokes  and  they  are  best  protected  by  overhead 
ground  wires  well  and  frequently  grounded  rather  than  by 
arresters. 

Induced  Strokes. — By  far  the  greater  number  of  disturbances 
in  transmission  systems  due  to  atmospheric  lightning  are  induced 
therein  by  discharges  between  clouds  overhead  or  between  a 
cloud  and  the  earth  in  the  vicinity. 
14  209 


210        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Surges. — Internal  surges  are  caused  by  any  change  in  the 
load  conditions.  They  may  be  either  transient  or  continuous. 
Transient  surges  are  caused  by  sudden  changes  of  loads  such  as 
are  occasioned  by  switching,  the  operation  of  circuit  breakers, 
etc.  They  are  usually  comparatively  unimportant  but  may  be 
quite  severe  where  a  very  heavy  current  is  broken  suddenly. 
Continuous  surges  are  caused  by  arcing  grounds  which  result  in 
occillations  of  great  power  at  a  frequency  usually  a  few  thousand 
cycles  per  second.  This  frequency  is  inherent  in  the  line  and 
is  determined  by  the  capacity,  resistance,  and  inductance  of  the 
line.  Surges  are  very  destructive  and  frequently  result  from 
breakdowns  of  insulation  caused  by  induced  lightning.  Light- 
ning arresters  (except  the  electrolytic  for  a  limited  time)  cannot 
handle  continuous  discharges  such  as  these  without  being 
destroyed  by  overheating.  Arresters  do  protect  against  arcing 
grounds,  however,  by  protecting  against  the  induced  surges 
that  are  their  primary  cause  in  so  many  cases. 

Displaced  Neutral. — On  a  transmission  line  another  cause  of 
trouble  that  results  in  a  continuous  high  voltage  is  a  displaced 
neutral  due  to  a  ground  on  one  phase  of  an  ungrounded  neutral 
system.  This  raises  the  voltage  of  the  other  phases  above 
ground  abnormally.  In  the  case  of  transformers  of  high  ratio 
this  effect  may  appear  even  on  the  opposite  side  of  the  trans- 
former and  cause  arresters  to  discharge  continuously  and  be 
destroyed  without  apparent  cause,  inasmuch  as  the  ground  may 
exist  a  great  distance  away  and  on  a  different  circuit. 

The  arresters  described  in  this  book  are  designed  to  take 
care  of  atmospheric  lightning  and  transient  internal  surges 
but  not  of  continuous  surges. 

Importance  of  Good  Ground. — Too  much  importance  cannot 
be  attached  to  the  making  of  proper  ground  connections.  These 
should  be  as  short  and  straight  as  possible.  A  poor  contact 
will  render  ineffective  every  effort  made  with  choke  coils  and 
lightning  arresters  to  divert  the  static  electricity  into  the  earth. 
It  is  important,  therefore,  not  only  to  construct  a  good  ground, 
but  in  doing  so  to  appreciate  thoroughly  the  necessity  of  avoiding 
unfavorable  natural  conditions.  Many  lightning  arrester  troubles 
are  traceable  directly  to  poor  ground  connections. 

Connection  to  Existing  Grounds. — Direct  connection  to  an 
underground  pipe  system  (such  as  a  city  water  main),  furnishes 
an  excellent  ground,  because  of  the  great  surface  of  pipe  in 


LIGHTNING  ARRESTERS 


211 


contact  with  the  moist  earth  and  the  maximum  number  of 
alternative  paths  for  the  discharge.  A  supplementary  ground 
line  should  always  be  connected  to  the  structural  steel  framework 
of  the  station,  and  to  any  nearby  trolley  rails.  In  water  power 
plants  the  ground  should  always  include  a  connection  to  the 
pipe  line  or  penstock  and  to  the  case  or  frame  of  the  apparatus 
to  be  protected. 

Ground  Conductor. — For  the  conductor  between  the  arrester 
and  the  ground  connection,  either  strap  copper  or  copper  tubing 
should  be  used.  It  is  important  that  a  conductor  having  the 
greatest  possible  superficial  area  be  used,  inasmuch  as  high 
frequency  discharges  are  carried  almost  wholly  on  the  surface  of 
the  conductor.  Strap  copper,  having  a  section  say  ^2  inch  by 
1^  inches,  makes  a  good  conductor  for  the  average  conditions. 
Such  a  ground  conductor  may  be  fastened  directly  to  the  station 
structure  with  wood  screws  The  course  of  the  ground  conductor 
should  be  direct  and  have  few  turns — the  fewer  the  better. 

D.C.  Arresters. — For  direct-current  service,  lightning  arresters 
are  required  for  comparatively  low  voltages,  but  of  high  discharge 
capacity.  The  most  satisfactory  arresters,  in  order  to  ade- 
quately protect  motors,  generators  and  converters,  must  have  the 
ability  to  discharge  static  at  the  lowest  possible  voltage  rise 
above  normal  operating  voltage,  without  danger  of  the  generator 
current  following  and  destroying  the  arrester.  In  general 
direct-current  arresters  are  of  two  kinds:  first,  those  which 
allow  the  generator  current  to  fol- 
low a  discharge  when  normal  volt- 
age is  established  and  then  disrupt  L^ 
it;  and,  second,  those  in  which 
the  generator  current  does  not 
follow  a  static  discharge.  The 
latter  type  requires  no  resistance 
in  the  static  discharge  path,  as  in 
the  case  of  the  first  type,  to  limit 
the  generator  current,  and  pro- 
vides the  greatest  freedom  for  dis- 
charge of  static  and  the  lowest 
voltage  discharge  point. 

Multipath  Arrester. — For  A.C.  or  D.C.  service  for  voltages  not 
exceeding  1000  a  "multipath"  arrester,  Fig.  132,  has  been 
developed  by  the  use  of  a  carborundum  block  fastened  between 


FIG. 


132. — Multipath    lightning 
arrester. 


212        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

the  two  terminal  plates  and  allowing  the  static  discharge  to  spread 
itself  over  a  number  of  minute  discharge  paths.  The  normal 
voltage  between  the  line  and  the  ground  is  divided  into  so  many 
minute  gaps  that  the  voltage  across  each  gap  is  too  small  to 
maintain  an  arc  after  the  discharge  has  passed. 

Condenser  Arrester. — One  form  of  condenser  arrester  consists 
of  a  condenser  alone;  the  other  consists  of  a  condenser  in  series 
with  a  spark  gap,  the  condenser  being  shunted  by  a  high  re- 
sistance. The  condenser  is  of  the  flat  plate  unit-form,  which, 
in  case  of  burnout,  is  easily  exchanged  without  the  necessity 
of  dismounting  the  arrester.  The  condensers  have  a  capacitance 
of  one  microfarad,  which  is  equivalent  in  capacity  to  100  miles  of 
average  line. 

In  the  arrester  without  gap  the  condenser  is  connected  directly 
across  from  line  to  ground,  whether  mounted  on  pole  or  car. 
Direct  current  cannot  pass  through  a  condenser,  and  there  is, 
therefore,  no  leakage.  The  condenser  is  charged  to  normal 
voltage,  but  as  soon  as  static  surges  appear  the  condenser  dis- 
charges these  surges  at  any  voltage  above  normal.  The  use  of  the 
arrester  without  gap  is  important  in  the  protection  of  apparatus 
having  weakened  insulation.  Many  railway  cars  are  operating 
with  motors  that  will  not  stand  a  breakdown  test  at  the  voltage 
necessary  to  bridge  an  arrester  gap,  but  with  this  type  of  arrester 
they  are  given  protection. 

In  the  arrester  with  gap  the  principal  differences  are  that  the 
condenser  is  always  discharged  and,  therefore,  affords  a  slightly 
increased  capacity  for  discharge  of  any  static  wave  of  great 
volume.  The  use  of  the  gap  also  provides  a  means  for  testing  the 
operation  of  the  arrester  by  the  use  of  tell  tale  papers  and  pro- 
vides an  easy  way  to  make  and  break  the  circuit  for  testing  the 
condenser. 

Non-arcing  Type. — One  of  the  first  successful  high  voltage 
arresters  for  A.C.  service  was  based  on  the  discovery  of  "non- 
arcing  metal "  by  Mr.  A.  J.  Wurts.  The  peculiar  property  of  this 
metal  is  that  an  alternating  current  will  not  maintain  an  arc 
between  adjacent  cylinders  of  this  metal,  provided  the  voltage  is 
not  too  high,  and  that  the  power  current  that  followed  the 
lightning  discharge  does  not  vaporize  too  much  of  the  metal.  The 
first  condition  was  met  by  having  a  fairly  large  number  of  very 
small  gaps  in  series,  and  the  second  condition  gave  no  trouble  on 
the  early  high  voltage  installations  where  the  amount  of  power 


LIGHTNING  ARRESTERS 


213 


Mounting  Iron  not  extend 
under  base  more  than  if 


current  was  comparatively  small.  For  large  amounts  of  power  it 
was  necessary  to  use  resistances  in  series  with  the  spark  gaps  to 
limit  the  current  and  these  resistances  reduced  the  effectiveness 
of  the  arresters.  For  very  high  voltages  different  schemes  were 
used  to  reduce  the  number  of  gaps  required  and  it  was  found  that 
by  shunting  a  certain  number  of  these  gaps  the  effectiveness  of  the 
arrester  was  increased. 

Fig.  133  shows  an  arrester  of  this  design  intended  for  service 
on  6600-volt  lines  where  the  capacity  does  not  exceed  2000 
K.V.A.  The  non-arcing  cyl- 
inders are  contained  between 
porcelain  insulators  in  such  a 
way  that  the  seven  cylinders  in 
each  of  the  two  sets  have  air 
gaps  of  about  ^2  inch  between 
adjacent  cylinders.  The  marble 
slab  forming  the  base  of  the 
arrester  also  has  mounted  on  it 
two  graphite  resistance  rods 
shunting  some  of  the  gaps. 
Modifications  of  this  scheme 
were  used  for  the  "low  equiva- 
lent/' "multigap,"  "multiphase" 
and  similar  "shunted  gap"  ar- 
resters that  were  installed  before 
the  electrolytic  arresters  were 

brought  out  and  which  are  still  giving  good  satisfaction  in  many 
plants  operating  at  voltages  as  high  as  88,000. 

Multi-chamber  Type. — The  arresters  previously  described  are 
a  few  of  the  many  types  made  by  the  Westinghouse  Electric  & 
Manufacturing  Company  for  moderate  voltage  circuits,  and  the 
General  Electric  Company  have  a  somewhat  similar  line  of 
arresters.  For  use  on  A.C..  systems  up  to  3000  volts  Schweit- 
zer &  Conrad  Inc.  build  the  multi-chamber  arrester  which 
consists  of  a  number  of  discharge  gaps  connected  in  series  with  a 
resistance  and  mounted  in  a  porcelain  housing.  This  housing  is  a 
porcelain  tube  closed  at  both  ends,  except  for  a  venting  hole  at  the 
lower  end.  The  mounting  bracket  is  an  integral  part  of  the  main 
housing  and  is  adapted  for  either  cross  arm  or  wall  mounting. 

Operation. — The  operating  element  of  the  arrester  consists 
of  five  series  gaps,  each  gap  being  mounted  in  a  separate  cylin- 


FIG.  133. — Non-arcing  arrester. 


214       SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

drical  chamber  in  a  block  of  insulating  material.  These  cylin- 
drical chambers  are  open  only  at  one  end,  and  the  discharge  gap 
in  each  chamber  is  located  near  the  closed  end. 

When  a  discharge  passes  through  this  arrester,  the  heated  air 
back  of  each  gap  in  the  closed  end  of  the  respective  chambers 
blows  the  arc  out  towards  the  open  end  of  the  chamber.  This 
blowout  action  is  very  effective  in  extinguishing  the  arc  and  in 
rupturing  the  dynamic  current  which  tends  to  follow  the  high 
voltage  discharge. 


FIG.  134. — Schweitzer  &  Conrad  multi-chamber  arrester. 

As  will  be  seen  from  Fig.  134,  the  insulating  blocks  are  as- 
sembled so  that  the  openings  of  adjacent  chambers  are  diametri- 
cally opposite  in  the  porcelain  tube,  making  the  path  between 
adjacent  gaps  a  maximum.  This  arrangement  prevents  bridging 
of  the  gaps  by  the  arc  or  the  arc  vapor.  The  spark  gap  points 
are  made  of  a  non-arcing  metal,  which  feature  assists  in  extin- 
guishing the  arc. 

Electrolytic  Type. — While  arresters  of  various  types  have  been 
developed  and  are  in  service  for  high  voltage  installations,  the 
electrolytic  arrester  has  been  found  to  furnish  the  maximum 


LIGHTNING  ARRESTERS 


215 


amount  of  protection  and  is  the  one  most  frequently  employed 
by  the  Westinghouse  Electric  &  Manufacturing  Company  and 
the  General  Electric  Company,  where  continuity  of  service  and 
value  of  the  equipment  to  be  protected  makes  it  advisable  to 
furnish  the  highest  grade  of  equipment. 


of  electrolytic  lightning  arrester. 

Arrangement. — The  essential  parts  of  an  electrolytic  lightning 
arrester  of  Westinghouse  design  are  shown  in  Fig.  135.  The  ar- 
rester consists  of  a  system  of  aluminum  cup  shaped  trays  (sup- 
ported on  a  porcelain  and  secured  in  frames  of  treated  wood) 
arranged  in  a  steel  tank.  The  system  of  trays  is  electrically 


216        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


connected  between  line  and  ground,  and  between  line  and  line. 
These  trays  contain  a  liquid  electrolyte  which  on  charging  the 
arrester  forms  a  film  on  their  surfaces.  This  film  prevents 
flow  of  current  at  normal  voltages,  but  forms  a  free  path  for 
abnormal  voltages  or  static  discharges.  Upon  cessation  of  the 
abnormal  stress  the  film  regains  its  original  resistance  practi- 
cally instantaneously,  and  prevents  power  current  from  following 
the  discharge. 

These  aluminum  trays  are  separated  from  each  other  by  por- 
celain spacers  arranged  around  the  edge  of  the  tray  insuring 
positive  separation  and  ample  space  for  the  escape  of  such  gases  as 
are  formed  during  a  heavy  discharge.  The  porcelain  spacers 
vary  slightly  in  thickness,  but  this  does  not  affect  the  operation 
of  the  arrester  because  the  resistance  of  the  cell  resides  primarily 

on  the  film  of  the  tray  and 
only  slightly  in  the  electro- 
lyte. The  trays  are  thoroughly 
treated  chemically  and  elec- 
trically and  are  shipped  out 
with  the  film  already  built  up. 
The  General  Electric  ar- 
resters have  the  same  main 
features  but  the  details  of 
construction  are  somewhat 
different. 

132  K.V.  Arrester.  — Fig. 
136  shows  the  arrangement 
of  tank  bushings,  trays  and 
supports  used  for  electrolytic 
arresters  for  132  K.V.  service. 
As  may  be  noted  the  tank  is 
elliptical  in  shape  with  two 
terminals,  the  longer  one  con- 
necting to  the  line  circuit, 
the  shorter  one  being  used 
for  the  neutral  connection. 

These  tanks  are  thoroughly  grounded  and  the  aluminum  trays 
are  mounted  on  insulated  supports  and  provided  with  barriers 
to  obviate  the  likelihood  of  any  high  voltage  jumping  from  the 
trays  through  the  oil  to  the  grounded  tanks. 

Gaps. — For  high  voltage  service,  horns  with  sphere  gaps  are 


FIG.  136. — Westinghouse  electrolytic 
lightning  arrester  132  K.V.  Assembly 
of  complete  pole  and  tray  column. 


LIGHTNING  ARRESTERS 


217 


provided  and  charge  and  discharge  resistors  furnished,  these  being 
connected  in  series  with  the  aluminum  trays  and  under  normal 
conditions  there  is  no  voltage  impressed  on  the  trays.  Abnormal 
voltage  or  high  frequency  surges  will  bridge  the  gaps  allowing 
current  to  pass  into  the  trays. 

The  horn-type  gap  was  first  used  and  is  still  employed  in  many 
cases.  It  is  so  arranged  that  any  arc  forming  will  follow  the 
natural  tendency  to  rise  and  will  be  extinguished  by  the  magnetic 
blowout  effect  and  the  increased  width  of  spacing  at  the  top  of 
the  horn. 

Sphere  Gaps. — A  sphere  gap  has  a  shorter  dielectric  spark  lag 
than  the  horn  gap,  i.e.,  it  has  a  greater  speed  of  discharge.  'The 
use  of  sphere  gaps  on  high  voltage  arresters  considerably  in- 
creases the  protection  afforded  the  apparatus.  On  the  lower 
voltage  arresters  the  rods  forming  the  horn  gaps  are  of  such  a 
diameter  that  they  have  practically  the  same  effect  as  sphere 
gaps;  i.e.,  the  gap  is  so  small  in  proportion  to  the  diameter  of  the 
horn  that  the  effect  is  the  same  as  if  sphere  gaps  were  used. 
Where  sphere  gaps  are  employed,  they  have  horn  extensions  rising 
above  the  spheres  to  assist  the  arc  to  rise  and  thus  be  quickly 
extinguished. 

\t 


FIG.  137.— Westinghouse  impulse  gap  for  arrester. 

Impulse  Gap. — The  latest  development  along  the  line  of  high 
speed  gaps  used  by  the  Westinghouse  Company  is  the  impulse 
gap  shown  diagrammatically  in  Fig.  137.  This  impulse  gap  is 


218         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

stated  to  excel  every  other  known  gap  in  assisting  arresters  to 
give  protection  from  lightning  and  other  high  frequency  or  high 
voltage  disturbance.  The  original  horn  gap  has  considerable 
time  lag,  allowing  high  frequency  surge  before  discharging  and 
giving  protection.  The  sphere  gap  partly  prevents  this  situation 
by  eliminating  the  time  lag  so  that  all  frequencies  are  discharged 
at  the  same  voltage.  The  impulse  gap  has  a  negative  time  lag, 
i.e.,  the  higher  the  frequency  the  lower  the  voltage  at  which  the 
gap  discharges.  Thus  the  impulse  gap  automatically  selects 
the  dangerous  surges  and  gives  protection  more  quickly  than  any 
other  known  form  of  gap.  With  the  impulse  gap  the  high  fre- 
quency discharge  voltage  may  be  as  low  as  two-thirds  or  even  one- 
third  of  the  normal  frequency  value.  It  is  therefore  possible  to 
use  a  gap  setting  that  will  permit  of  the  desired  degree  of  pro- 
tection against  dangerous  surges  and  not  permitting  too  frequent 
discharging  on  minor  surges  at  normal  frequency. 

Gap  Speed. — The  high  speed  of  the  sphere  gap  as  compared 
with  the  horn  gap  is  due  to  the  elimination  of  the  time  required 
to  build  up  a  sphere  of  equi-potential  surface  on  the  discharge 
part  of  the  horn  gap.  The  sphere  of  the  sphere  gap  provides  at 
once  for  this,  and  practically  eliminates  corona.  It  does  not, 
however,  give  the  desired  protection  against  the  steep-wave 
front  or  high  frequency  surges  due  to  its  in- 
ability to  discharge  these  disturbances  at 
lower  voltages  than  the  normal  frequency 
setting  of  the  gaps. 

In  the  impulse  gaps,  however,  the  advan- 
tage  of  high  normal  frequency  setting  of  the 
^ps  can  be  had  without  the  corresponding 
disadvantage  of  reduced  protection,  since 
the  high  frequency  breakdown  value  of  the  impulse  gaps  is 
much  lower. 

The  schematic  diagram  of  the  impulse  gaps  is  shown  in  Fig. 
138.  This  impulse  gap  uses  a  circuit  that  at  normal  frequency  is 
balanced  as  to  voltage,  but  becomes  unbalanced  and  starts  a 
discharge  in  case  of  any  high  frequency  surges.  At  normal 
frequency  there  is  no  difference  of  potential  between  the  mid- 
point of  the  condenser  and  the  auxiliary  electrode  midway  be- 
tween the  auxiliary  horn  and  sphere  gaps.  A  high  frequency, 
however,  passes  freely  through  the  condensers  and  piles  up  its  full 
voltage  across  the  resistance  and  carries  across  one-half  of  the 


LIGHTNING  ARRESTERS 


219 


total  gap.  This  gap,  therefore,  breaks  down,  resulting  in  the 
total  voltage  being  impressed  on  the  remaining  gap  which  breaks 
down  in  turn.  Breakdown  at  each  half  of  the  gap  is  facilitated 
by  the  fact  that  the  auxiliary  electrode  is  small  in  size,  having 
needle  gap  characteristics  so  that  the  discharge  voltage  at  each 
half  of  the  gap  is  about  Y±  rather  than  Y^  of  the  total  gap 
between  the  spheres. 

Oxide  Film. — Owing  to  the  use  of  the  liquid  electrolyte,  the 
necessity  for  periodical  charging  and  the  comparatively  high 
price  of  the  aluminum  cell  electrolytic  arrester,  the  oxide  film 
arrester  has  been  developed  by  the  General  Electric  Company 
who  have  had  some  in  service,  experimentally,  for  some  time 
and  have  lately  placed  them  on  the  general  market.  This  oxide 
film  arrester  depends  for  its  functioning  on  the  fact  that  certain 
dry  chemical  compounds,  such  as  lead  peroxide,  can  be  changed 
rapidly  from  a  very  good  conductor  to  an  almost  perfect  non- 
conductor, litharge,  by  the  application  of  a  slight  degree  of  heat, 
such  as  would  be  caused  by  the  passage  of  a  lightning  discharge. 


FIG.   139. — Cylindrical  choke  coil. 


Choke  Coils. — Whenever  a  surge  of  high  frequency  or  steep- 
wave  front  due  to  lightning  or  any  other  cause  travels  along  a 
line  and  strikes  an  inductive  winding,  it  builds  up  a  high  voltage 
to  ground.  Choke  coils  are  frequently  furnished  for  use  on  line 
circuits  to  take  the  brunt  of  such  surges  and  to  provide  a  point 
where  the  lightning  arresters  can  be  connected  in  to  secure  the 
maximum  protective  effect.  Besides  relieving  the  end  turns  of 
the  power  apparatus  from  the  first  shock  of  the  surge  and  flatten- 
ing it  out  before  it  can  enter  the  power  apparatus,  it  delays  the 
progress  of  the  surge  and  the  piling  up  of  the  voltage  moment- 


220         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

arily  at  the  line,  thus  giving  the  arrester  more  time  and  more 
tendency  to  discharge  and  relieve  the  line. 

While  a  very  small  choke  coil  has  low  protective  power,  very 
large  coils  will  introduce  excessive  reactance  in  the  line  and  impair 
the  regulation.  It  is,  necessary  therefore,  to  choose  for  any 
service  a  choke  coil  proportioned  to  the  needs  of  the  apparatus. 

Cylindrical  Coil. — Fig.  139  shows  a  choke  coil  suitable  for 
50  K.V.  operation.  The  coil  consists  of  20  turns  of  aluminum 
rod  formed  into  a  cylinder  15  inches  in  diameter,  and  provided 
with  bracing  clamps  to  rigidly  separate  the  turns  and  to  give 
mechanical  strength  to  the  helix.  Similar  coils  9  inches  in  diame- 
ter can  be  supplied  having  a  fewer  number  of  turns  and  approxi- 
mately one-sixth  the  impedance. 

Horn  Arresters. — For  plants  of  moderate  capacity  for  outdoor 
high  voltage  service,  particularly  where  the  lightning  conditions 
are  not  very  severe,  the  cost  of  electrolytic  lightning  arresters 
may  not  be  justified  by  the  value  of  the  equipment  which  they 
are  protecting.  For  such  cases,  horn  type  lightning  arresters 
can  be  utilized  to  advantage. 

Railway  Industrial  &  Engineering  Type. — Such  arresters  made 
by  the  Railway  &  Industrial  Engineering  Company  are  usually 
combined  with  triangular  shaped  choke  coils  as  shown  in  Fig.  140. 
With  this  arrangement,  one  side  of  the  choke  coil  acts  as  one 
of  the  horns  of  the  arrester.  The  coil  is  used  in  this  way,  first  as 
a  magnetic  blowout  to  hasten  the  travel  of  the  arc  up  the  horns, 
and  second  to  increase  the  speed  of  operation  of  the  arrester. 
The  incoming  line  is  connected  to  the  outside  turn,  and  the  path 
of  the  power  circuit  is  around  the  coil  and  out  through  the  center, 
so  that  the  surge  entering  the  coil  meets  its  first  obstruction  at 
the  first  sharp  upward  turn  of  the  coil  opposite  which  is  mounted 
the  ground  horn.  The  voltage  will  build  up  at  this  point  and 
is  reflected  back  by  the  other  turn  toward  ground.  Due  to  this 
construction  the  gaps  to  ground  may  be  set  approximately  50  per 
cent,  greater  than  the  ordinary  shunted  horn  gaps  with  the  same 
protection  obtained. 

For  more  severe  lightning  conditions  the  type  of  horn  arrester 
shown  in  Fig.  141  is  used.  This  arrester  is  similar  to  the  one 
previously  described  except  that  a  reactance  coil  is  connected 
in  series  with  the  high  capacity  resistance  in  the  ground  circuit. 
An  auxiliary  horn  gap  shunts  both  the  reactance  coil  and  the 
resistance  thus  giving  a  direct  path  to  ground  to  a  surge  of  such 


LIGHTNING  ARRESTERS 


221 


FIG.  140. — Railway  &  Industrial  Engr.  Co.  lightning  arrester  type  "WB. 


FIG.   141. — Railway  &  Industrial  Engr.  Co.  arrester  with  resistor. 


222         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


capacity  that  it  cannot  be  discharged  quickly  enough  through  the 
reactance  and  resistance.  This  reactance  is  used  principally  to 
relieve  the  resistance  of  the  heavy  strain  by  smoothing  out  the 
surge  before  it  reaches  the  resistance.  The  use  of  the  reactance 
coil  in  no  way  interferes  with  sensitiveness  of  the  arrester. 

S.  &  C.  Horn  Type. — Horn-gap  arresters  are  also  built  by 
Schweitzer  and  Conrad  in  the  form  of  the  graded  resistance  arrester 
which  consists  essentially  of  a  horn  gap  and  a  number  of  resis- 
tance units  so  arranged  that  as  the  arc  rises  from  the  lower  part 
to  the  upper  part  of  the  horn,  the  resistance  is  automatically  cut 
into  circuit  step  by  step,  so  that  the  current  is  rapidly  cut  down 
and  the  arc  is  easily  broken  when  it  reaches  the  upper  part  of 
the  horn.  See  Fig.  142. 


ISOLATING 
TUBES 
CONTAINING 
•ilASCE 


FIG.  142. — Schweitzer  &  Conrad  graded  resistance  lightning  arrester. 

With  any  potential  rise  on  the  line  or  apparatus  protected  by 
the  arrester,  the  arc  will  start  across  the  smallest  gap  which  has 
all  the  resistance  in  series.  If  the  potential  rise  is  of  low  energy 
capacity,  the  current  flowing  through  this  gap  and  total  resistance 
may  be  sufficient  to  keep  the  voltage  down  to  approximately 
normal.  If  the  current  flowing  through  this  gap  and  resistance  is 
insufficient  to  keep  the  voltage  down,  the  arc  will  break  across  the 
next  lower  step  and  a  larger  current  will  flow.  If  this  current  is 
still  insufficient  to  keep  the  voltage  down  to  safe  value,  then  the 
next  lower  step  will  arc  across,  etc.,  until  the  "no  resistance" 


LIGHTNING  ARRESTERS 


223 


or  lowest  step  is  reached,  when  the  system  will  actually  be  short- 
circuited  and  practically  unlimited  current  can  flow. 

Schweitzer  &  Conrad  arresters  are  regularly  furnished  in  a 
number  of  combinations.  By  the  addition  of  a  choke  coil,  a 
disconnecting  switch,  and  a  load  fuse,  a  complete  protective  com- 
bination can  be  made  on  one  channel  base,  so  that  the  installa- 
tion of  the  whole  combination  is  quite  simple  as  compared  to  the 
installation  of  separate  pieces  of  apparatus.  One  of  these  ar- 
rangements is  shown  on  Fig.  143. 


FIG.  143. — Schweitzer  &  Conrad  protective  combination. 

Reactors. — Choke  coils,  in  addition  to  being  used  for  lightning 
protection,  are  employed  for  the  purpose  of  current  limiting 
reactors  in  large  power  plants,  and  have  been  connected  in  the 
circuits  of  generators,  feeders  and  bus  bars. 

In  large  systems  current  limiting  reactors  have  been  installed 
for  the  purpose  of  limiting  the  amount  of  current  that  may  flow 
from  any  part  of  the  system  into  a  short  circuit  in  the  apparatus 
or  the  connections  inside  the  station  or  close  to  the  station.  By 
so  limiting  the  abnormal  flow  of  current  into  a  short  circuit,  the 
generating  system  as  a  whole  is  relieved  from  the  possible  disas- 
trous effects  of  short  circuit.  At  the  time  of  the  disturbance  on 
the  system  the  extra  load  thrown  on  the  generators  by  the  energy 
fed  into  the  short  circuit  is  such  that  the  generating  frequency 
and  voltage  are  momentarily  lowered  and  the  reactors  will  tend 
to  reduce  this  extra  load  on  the  system  and  minimize  the  change 


224         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

in  frequency  that  often  throws  out  of  step  the  synchronous 
apparatus  in  the. substations  and  the  generators  at  other  connect- 
ed stations. 

Some  of  the  earlier  turbogenerators  particularly  for  25-cycle 
service,  had  a  comparatively  small  amount  of  internal  reactance, 
but  the  manufacturers  of  turbogenerators  are  now  recommending 
a  total  generator  reactance,  internal  and  external,  of  from  10  to  15 
per  cent,  and  turbogenerators  are  now  usually  so  designed  as  to 
be  able  to  withstand  mechanically  a  dead  short  circuit  across  their 
terminals  with  full  field  excitation.  Arrangements  are  usually 
made  to  build  such  turbogenerators  with  fairly  high  internal 
reactance  and  to  brace  their  coils  sufficiently  to  withstand  the 
mechanical  stresses  set  up  at  the  time  of  short  circuit. 

Breakdowns. — Experience  seems  to  show  that  a  large  percent- 
age of  the  breakdowns  originate  in  the  feeder  circuits,  and  the 
use  of  feeder  reactors  for  minimizing  the  trouble  is  employed 
in  many  cases.  These  feeder  reactors  reduce  the  stresses  upon 
the  circuit  breakers,  and  frequently  make  it  possible  to  use 
smaller  and  cheaper  breakers  in  moderate  capacity  plants 
than  would  otherwise  be  possible.  As  the  ratio  of  the  feeder 
capacity  to  the  total  station  capacity  in  large  plants  is  usually 
small,  a  small  percentage  reactance  on  a  small  feeder  reduces 
the  short-circuit  current  to  practically  a  negligible  quantity. 
The  small  percentage  of  reactance  also  makes  negligible  the  effect 
of  the  regulation  of  the  feeder. 

With  reduction  in  the  feeder  short-circuit  current,  the  relay 
system  can  be  made  far  more  selective,  the  voltage  in  the  system 
will  not  be  materially  affected,  the  energy  fed  into  the  short 
circuit  will  not  tend  to  slow  the  generators  down,  reducing  a 
change  in  the  system  frequency,  and  synchronous  apparatus 
on  other  parts  of  the  system  will  not  fall  out  of  step.  The 
protected  feeder  will  be  automatically  disconnected  from  the 
system  without  interruption  of  service  to  the  remainder  of 
the  system. 

Makers. — Current  limiting  reactors  for  various  services  have 
been  furnished  to  many  of  the  largest  plants  by  the  Metropolitan 
Engineering  Company,  the  General  Electric  Company  and  the 
Westinghouse  Electric  &  Manufacturing  Company. 

Metropolitan  Engineering  Company  Reactors.— The  appear- 
ance of  the  coils  is  clearly  shown  in  Fig.  144,  this  showing 
an  installation  of  porcelain-clad  reactors  of  the  Metropolitan 


LIGHTNING  ARRESTERS  225 

Engineering  Company.  The  coil  consists  of  a  series  of  horizon- 
tally wound  spirals  supported  and  insulated  by  porcelain  arms 
having  suitable  recesses  for  the  winding.  The  arms  are  assembled 
radially  as  vertical  walls  between  a  hollow  core  of  concrete 
or  soapstone,  and  an  outer  enclosing  wall  built  up  of  special 
porcelain  segments.  These  cellular  compartments,  so  formed, 
allow  natural  ventilation  for  the  coil.  The  entire  coil  is  supported 
at  the  two  ends  by  heavy  concrete  headers  securely  held  by  a 


FIG.  144. — Reactor  of  Metropolitan  Engineering  Co. 

number  of  brass  bolts  with  insulating  mica  tubes  passing  through 
the  heads  and  wall  of  the  special  porcelain  segments  from  top  to 
bottom.  Ventilating  holes  are  connected  with  each  vertical 
cellular  compartment  of  the  coils. 

Porcelain  Clad. — These  reactance  coils  are  porcelain  clad, 
and  the  windings  are  embedded  at  their  supports  in  walls  of 
smooth  porcelain  insulators,  giving  fireproof  construction  with 
good  electrical  and  mechanical  qualities  entirely  unaffected  by 
high  temperatures.  The  smooth  glazed  finish  of  the  porcelain 
facilitates  inspection  and  cleaning  of  coils,  and  the  almost  mono- 
lithic construction  insures  mechanical  safety. 

Mutually  Reactive  Coils. — For  combining  in  one  unit  the 
protection  desirable  for  the  circuit  of  the  generator  bus  bar  and 
feeder,  mutually  inductive  reactors  have  been  designed,  these 
consisting  essentially  of  reactors  with  a  tap  in  the  middle,  the 
current  being  taken  in  at  this  point  and  taken  out  at  the  two 
opposite  ends  as  shown  diagrammatically  in  Fig.  145.  These 


226         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


mutually  inductive  reactors  protect  the  generator  from  excessive 
short-circuit  currents,  protect  and  localize  any  trouble  on  a  bus 
section,  and  materially  reduce  the  short-circuit  current  into 
feeder  troubles. 


1M-HI IN 

EP|EH  IGRO|UP    BJJ5         1  o    o|  1 


FIG.   145. 

This  combined  system  of  coils  is  better  than  the  independent 
coils,  in  requiring  much  less  space,  in  utilizing  the  mutual  inductance 
between  the  two  sections  of  the  coils  to  limit  the  current  to  a  great- 
er extent  for  a  given  amount  of  copper,  and  to  reduce  the  short-cir- 
cuit disturbance,  as  the  current  in  the  short  circuit  is  made  to 
keep  up  the  pressure  on  the  rest  of  the  system. 

In  all  cases  the  reactance  coils  should  be  placed  as  close  to  the 
bus  as  possible  to  protect  the  bus  under  the  greatest  number  of 
conditions,  so  that  the  reactance  coils  should  be  considered  as  a 
part  of  and  made  as  reliable  <as  the  high  tension  bus. 

Semi-porcelain  Clad. — A  modification  in  the  construction 
of  these  Metropolitan  coils  is  known  as  the  semi  porcelain  clad 
reactor.  With  this  arrangement  the  coils  are  made  up  of  a  num- 
ber of  concentric  co-axial  solenoids  in  parallel,  designed  to  give  a 
uniform  potential  gradient  from  top  to  bottom.  The  insulating 
space  required  between  layers  is  practically  eliminated,  this 
resulting  in  a  large  reduction  in  size  and  increased  efficiency 
of  coils.  While  the  coils  are  cylindrical  they  are  assembled  in 
rectangular  forms  with  porcelain  insulators  at  the  four  corners, 
these  insulators  being  of  L  shape  with  micarta  barriers  passing  in 
front  of  the  coils. 

G.  E.  Reactors. — General  Electric  reactors  are  of  the  "cast  in" 
type,  i.e.,  the  windings  are  rigidly  held  in  place  by  vertical  con- 
crete supports  which  are  cast  around  the  turns  after  the  coil 


LIGHTNING  ARRESTERS 


227 


has  been  wound  in  a  form  built  up  of  steel  plates  as  shown  in 
Fig.  146.     After  the  concrete  has  set,  the  forms  are  removed  and 


t> 


& 


the  concrete  is  cured  by  treating  with  high-pressure  steam.     This 
method  will  give  twice  as  much  aging  as  would  be  obtained  by 


228         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

natural  processes  in  several  months.  The  reactor  is  then  sand 
blasted,  thus  giving  both  the  copper  and  concrete  a  very  finished 
appearance  as  shown  in  Fig.  147. 

The  number  of  supports  depends  upon  the  current  rating 
and  the  stresses  produced  by  short  circuit  current.  Intimate 
contact  between  the  winding  and  the  supports  insures  a  very 
rigid  structure.  There  are  no  through  bolts  in  the  coil,  and  the 
possibility  of  a  short  circuited  winding  due  to  arc  over  from  the 
terminals  to  the  bolts  is  therefore  eliminated. 


iffir intent 

*jjL$         ^5  25 

'^  JHjF-*~ •l^^r  «-*   '^  -  '  ~-~    -%~ 

t  *  ^^i 


FIG.  147. — G.  E.  Co.  "cast  in"  type  power  limiting  reactors. 

Windings. — The  windings  consist  of  one  or  more  cables  in 
multiple.  These  may  be  solid  or,  if  necessary,  concentrically 
stranded  with  asbestos  paper  between  layers  in  order  to  keep  to  a 
minimum  the  loss  due  to  eddy  currents. 

The  turns  are  wound  radially  in  conical  layers  with  adjacent 
layers  inclined  in  opposite  directions.  Ample  spacing  is  provided 
between  turns  and  layers,  depending  upon  the  circuit  voltage 
and  the  K.V.A.  capacity  of  the  reactor.  Any  two  adjacent  layers 
converge  toward  the  point  of  interconnecting  crossover,  where 
the  voltage  between  layers  is  consequently  equal  to  the  voltage 
between  turns.  All  crossovers  are  embedded  in  the  concrete 
supports  so  that  all  of  the  cable  exposed  is  concentric,  and  full 
distance  is  maintained  between  turns  at  these  points. 

The  terminals  consist  of  heavy  pressed  copper  tube  brought 
out  radially  or  circumferentially  from  one  of  the  coil  supports. 
The  conductors  are  brazed  into  these  terminals,  thereby  eliminat- 
ing the  possibility  of  an  open  circuit  at  these  points,  due  to  over 
heating  by  short  circuit  current. 


LIGHTNING  ARRESTERS  229 

If  necessary  the  coil  may  be  divided  into  two  sections  wound 
in  opposite  directions,  in  which  case  the  bottom  end  of  the  top 
section  and  top  end  of  the  bottom  section  are  usually  brought 
to  the  same  terminals,  and  the  other  ends  of  the  sections  are 
each  brought  to  a  terminal  which  is  bolted  to  a  vertical  copper 
bar  or  strap  joining  the  two.  Thus  the  coil  is  symmetrical 
about  a  plane  perpendicular  to  the  mid  point  of  its  vertical  axis. 

Base. — The  concrete  supports  are  uniformly  spaced  around  the 
coil.  They  rest  on  a  heavy  concrete  base  ring  having  a  rectangu- 
lar cross  section,  which  serves  to  distribute  the  weight  of  the 
coil.  The  supports  and  base  are  bolted  together  by  means  of 
bolts  fitting  into  threaded  thimbles  cast  in  the  bottom  of  each 
support. 

Insulators. — To  insulate  the  structure  from  ground  the  base  is 
set  on  pedestal-type  porcelains  to  which  castings  are  fitted  at 
each  end.  The  top  castings  are  provided  with  tap  holes  in  the 
center  by  means  of  which  they  may  be  bolted  to  the  base  ring. 
The  bottom  castings  are  provided  with  holes  for  bolting  to  the 
floor. 

Installation. — For  a  three  phase  installation,  three  single  phase 
reactors  may  be  installed  in  a  row,  at  the  corners  of  an  equilateral 
triangle,  or  one  above  the  other.  When  required  by  the  magnetic 
forces  the  reactors  are  braced  from  each  other  and  from  the  wall 
by  means  of  corrugated  porcelains  which  fit  into  castings  attached 
to  the  concrete  columns.  A  three-phase  reactor  may  also  con- 
sist of  three  separate  windings  one  above  the  other,  cast  into  the 
same  supports.  Where  space  is  available,  the  preferred  method 
however,  is  to  install  each  reactor  in  a  separate  cell. 

Shunting  Resistance. — In  some  of  the  latest  designs,  the  reactors 
are  supplied  with  shunting  resistors  connected  across  the  termi- 
nals of  the  coil.  These  resistors  will  absorb  impulse  voltages  and 
prevent  the  building  up  of  excessive  resonant  voltages.  Under 
normal  conditions,  the  loss  in  the  resistor  is  very  small,  but 
in  case  of  high  frequency  surges,  the  shunting  path  is  very 
desirable  in  that  it  tends  to  dissipate  the  energy  of  the  high 
frequency  oscillation.  It  is  an  interesting  fact  that  these 
resistors  have  the  valuable  property  of  high  resistance  at  low 
voltages  and  low  resistance  at  high  voltages.  The  resistors 
consist  of  resistance  rods  embedded  in  concrete  blocks  which 
are  placed  inside  the  reactor  and  rest  upon  the  reactor  base. 


230         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


Westinghouse  Reactors. — The  current  limiting  reactors  of  the 
Westinghouse  Electric  &  Manuf  acuring  Company  are  built  either 
as  single-phase  units  or  as  3-phase.  A  typical  single-phase  coil 
is  shown  in  Fig.  148,  this  having  a  rating  of  100  K.V.A.,  1000 
amperes,  25  cycles  or  8  per  cent,  on  the  basis  of  a  normal  3- 
phase  circuit,  at  2200  volts  with  one  coil  per  phase.  As  these 

current  limiting  reactors  are  air 
cooled  a  comparatively  large  area 
of  conductor  surface  must  be 
provided  to  dissipate  the  PR  loss 
and  since  the  area  of  a  conductor, 
such  as  a  cable,  increases  with  the 
square  of  the  diameter  and  the 
surface  as  the  first  power,  it  is 
obvious  that  the  smaller  the 
diameter  of  the  cable  the  more 
efficiently  is  the  copper  worked. 
The  copper  represents  the  large 
part  of  the  cost  of  a  reactor  hence 
the  necessity  to  keep  its  amount  to 
a  minimum.  This  reasoning  has 
led  to  the  use  of  a  fairly  small  size 
of  cable  and  the  use  of  a  number  of 
these  in  parallel  to  get  the  proper 
current-carrying  capacity. 
Multiple  Winding. — With  a  number  of  cables  in  multiple  in  a 
coil  of  this  kind  there  is  a  tendency  for  these  parallel  circuits  to 
have  different  ohmic  and  inductive  characteristics  unless  special 
precautions  are  taken  to  see  that  the  lengths  and  relative  posi- 
tions of  the  cables  in  the  parallel  paths  are  practically  identical. 
If  this  is  not  done  there  will  be  circulating  currents  set  up  that 
will  cause  excessive  loss  and  heating  of  the  coils. 

Large  Reactors. — With  a  typical  single-phase  Westinghouse 
coil  for  use  with  a  3-phase  generator  of  21,100-K.V.A.  capacity 
the  normal  full-load  current  is  1100  amperes  and  the  coils  are 
wound  with  seven  stranded  bare  copper  cables  connected  in 
parallel  in  such  a  manner  that  the  paths  are  of  substantially  the 
same  lengths  and  impedance.  The  seven  cables  are  wound  into 
grooves  in  specially  prepared  moulded  fireproof  cleats  These 
seven  cables  enter  the  coils  at  seven  equi-distant  points  around 
the  inner  periphery  of  the  bottom  layer  of  the  coil.  The  first 


FIG.  148. — Westinghouse   single- 
phase  reactor. 


LIGHTNING  ARRESTERS 


231 


cable  occupies  the  inner  circumferencial  row  of  slots  for  one- 
seventh  of  a  turn  and  then  passes  out  to  the  second  row  of  slots 
and  the  second  cable  occupies  the  inner  row.  These  two  con- 
tinue in  this  position  for  the  second  seventh  turn,  at  the  end  of 
which  they  step  outward  one  more  row  and  the  third  cable  enters 
on  the  inner  row. 

The  moulded  cleats  with  slots  into  which  the  cable  is  wound 
have  holes  in  their  ends  through  which  brass  rods  covered  by 
insulating  tubes  are  placed  for  clamping  the  layers  together 
securely.  On  the  top  and  bottom  of  each  tier  of  cleats  is  placed 
a  nonmagnetic  metal  cleat  that  allows  the  coil  to  be  clamped 

tightly  together.     The  spacing  be- 

tween  columns  of  cleats  is  close 
enough  to  prevent  any  appreciable 
deflection  of  the  cable  under  the 
most  severe  short-circuit  conditions. 
The  tensile  strength  of  the  copper 
in  the  cable  is  sufficient  to  resist  the 
magnetic  stress  tending  to  increase 
the  diameter  of  the  coil. 

Supports. — The  coil  is  supported 
on  three  nonmagnetic  castings  each 
of  which  spans  four  tiers  of  cleats. 
Into  these  castings  are  cemented 
insulators  which  rest  on  metal  pins 
suitable  for  cementing  or  bolting  to 
the  floor.  Two  brass  rods  pass 
through  the  opening  of  the  coil  and 
are  supported  by  porcelain  bush- 
ings held  in  place  by  a  three  way 
support  and  on  each  end  of  the  rod 
is  provided  a  line  terminal.  All  of 
the  cables  at  one  end  of  the  coil  are 

connected  to  one  rod  while  the  cables  at  the  other  end  connect 
to  the  second  rod. 

Three-phase  Reactor. — For  3-phase  feeder  circuits  of  mod- 
erate capacity  a  3-phase  reactor  such  as  shown  in  Fig.  149 
can  be  supplied.  This  shows  a  440-ampere,  127-volt,  167- 
K.V.A.  25-cycle,  3-phase  coil  for  use  on  a  6600-volt  circuit. 
Such  a  coil  gets  the  advantage  of  the  mutual  reactance  between 
phases  and  it  may  be  noted  that  the  coils  at  the  top  and  bottom 


FIG.  149. — Westinghouse  three- 
phase  feeder  reactor. 


232         SWITCHING  EQUIPMENT  FOR  POW^R  CONTROL 

are  part  of  the  same  coil  in  one  phase  while  the  two  wider  coils 
in  the  middle  are  for  the  remaining  phases.  Such  3-phase 
coils  can  be  installed  in  a  much  smaller  space  than  three  single- 
phase  independent  coils  and  the  wiring  of  the  plant  can  fre- 
quently be  simplified  by  their  use. 


CHAPTER  IX 
REGULATORS 

The  switches,  fuses,  circuit  breakers,  relays,  instruments, 
etc.,  all  have  their  important  functions  to  perform  as  part  of  the 
switch  gear  in  a  station  but  as  practically  all  electrical  energy 
is  distributed  on  the  constant  potential  system,  the  devices 
for  maintaining  constant  potential  are  of  vital  importance  in 
any  plant.  Where  the  circuits  are  few  and  all  of  about  the 
same  length  and  load  conditions  it  is  only  necessary  to  maintain 
constant  the  voltage  on  the  bus  bars.  Where  there  are  many 
feeders  with  varying  load  conditions  it  becomes  a  matter  of 
importance  to  be  able  to  adjust  the  voltage  on  these  feeders 
independently.  The  demand  for  this  class  of  adjustment  led 
to  the  development  of  feeder  regulators. 

FEEDER  REGULATORS 

Step  Type  Regulator. — The  first  type  of  regulator  was  a 
transformer  with  many  taps  and  provision  for  connecting  the 
feeder  to  any  tap.  This  could  be  done  by  switches  of  various 
kinds  and  the  natural  development  was  to  arrange  the  contacts 
in  the  form  of  a  ring  on  a  suitable  faceplate  and  to  provide  a 
movable  arm  for  connecting  the  feeder  to  any  of  the  taps  from 
the  transformer.  As  the  voltage  was  varied  by  definite  steps,  this 
type  of  regulator  was  known  as  the  step  type  regulator.  These 
regulators  consist  essentially  of  a  dial  or  drum  with  a  number 
of  contacts  or  steps,  connecting  to  taps  brought  out  from 
the  secondary  of  a  transformer  whose  primary  is  usually  connect- 
ed across  the  feeder  circuit.  This  feeder  circuit  is  connected 
in  series  with  the  dial  and  a  reversing  switch  so  that  a  part  or 
all  of  the  secondary  voltage  of  the  transformer  can  be  added  to 
or  taken  from  the  bus  voltage. 

Reverser. — The  moving  arm  on  the  dial  type  regulator  is 
usually  arranged  so  that  in  passing  from  the  position  of  maximum 
boost  the  number  of  secondary  turns  in  series  with  the  circuit 
is  reduced  in  equal  steps  until  the  turns  are  all  cut  out.  Further 
rotation  in  the  same  direction  throws  over  the  reversing  switch 

233 


234         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

and  then  cuts  in  the  same  secondary  turns  in  opposition  to  the 
main  voltage  until  the  position  of  maximum  buck  is  reached, 
when  a  stop  prevents  any  further  rotation  in  that  direction.  A 
similar  stop  prevents  overtravel  in  the  position  of  maximum 
boost 

Split  Arm. — With  this  dial  type  regulator  the  contacts  are 
mounted  on  a  marble  dial  and  a  movable  arm,  spring  actuated, 
is  so  arranged  that  it  moves  quickly  from  step  to  step  without 
any  possibility  of  stopping  between  steps  and  short-circuiting 
a  part  of  the  transformer.  A  modification  of  this  arrangement 
has  the  contact  arm  split  in  two  parts  with  a  preventive  resistor 
or  reactor  joining  the  two  parts  to  obviate  any  chance  of  short- 
circuiting  part  of  the  transformer. 

Limits. — For  high  voltage  or  heavy  current  capacity  the  step 
type  regulator  can  be  employed  by  the  use  of  current  or  po- 
tential transformers  or  both,  so  that  the  current  to  be  handled 
does  not  exceed  200  amperes  and  the  voltage  on  the  dial  is  not 
greater  than  about  2200  volts  or  about  440  K.W.  maximum  for 
the  capacity  of  the  feeder  on  which  20  per  cent,  regulation  or 
88  K.W.  can  be  obtained. 

For  heavy  service  on  circuits  up  to  6600  volts  and  for  handling 
a  greater  voltage  per  step  than  the  20-25  that  can  be  taken 
care  of  with  an  open  air  dial,  a  drum-type  regulator  is  used  having 
its  switch  and  contacts  immersed  in  oil.  Regulators  of  this  type 
can  be  built  for  6600  volts,  200  amperes,  20  per  cent,  regula- 
tion or  about  three  times  the  capacity  of  the  dial  type.  For  some 
classes  of  electric  furnace  work  the  drum-type  regulator  or  a 
step  by  step  device  is  employed  with  an  induction  regulator  to 
give  a  smooth  and  continuous  variation  in  voltage  between  steps. 

Induction  Type. — In  most  modern  installations  the  induction 
regulator  is  used  in  preference  to  the  step  type  as  giving  a  more 
even  adjustment  of  voltage,  avoiding  any  winking  of  the  lights 
and  allowing  for  automatic  operation  in  a  simpler  manner 
than  the  step  type. 

Induction  type  regulators  are  made  for  single-phase  or  3- 
phase  service  and  arranged  for  hand  operation  or  motor  oper- 
ation, or  motor  operation  controlled  from  a  distant  point,  or 
for  complete  automatic  operation  by  means  of  relays.  The 
regulator  for  single  phase  circuits  consists  of  a  rotatable  primary 
core  and  winding  and  a  fixed  secondary  core  and  winding  usually 
immersed  in  oil.  The  primary  winding  is  connected  across 


REGULATORS 


235 


the  line  and  the  secondary  is  in  series  with  the  feeder.  The 
voltage  induced  in  the  secondary  depends  on  the  relative  posi- 
tion of  the  two  coils  and  increases  or  decreases  the  feeder  voltage 
by  a  practically  infinite  number  of  steps. 

Where  automatic  operation  is  desired  for  either  single  or 
3-phase  regulation  this  is  obtained  by  the  action  of  a  voltage 
relay  either  with  or  without  a  compensating  device.  This 
relay  acts  in  conjunction  with  the  motor  on  the  regulator  in 
such  a  way  that  as  the  load  comes  on  or  as  the  bus  voltage  drops 
the  motor  will  turn  the  regulator  in  such  a  direction  as  to  increase 
the  voltage.  By  means  of  a  compensator,  which  can  be  set 
for  a  certain  ohmic  and  a  certain  inductive  drop,  the  voltage  at 
the  point  of  distribution  can  be  maintained  constant,  independent 
of  the  amount  and  power  factor  of 
the  load  if  the  total  drop  is  within 
the  range  of  the  regulator. 

While  the  illustrations  and  de- 
scriptions of  induction  regulators 
that  follow  are  based  on  Westing- 
house  apparatus,  the  regulators  made 
by  the  General  Electric  Company 
have  many  of  the  same  features  and 
the  descriptions  with  slight  modifi- 
cations would  apply  in  most  cases  to 
the  General  Electric  devices. 

Single  phase  Type. — Fig.  150 
shows  a  motor  operated  single-phase 
induction  type  regulator  with  the 
tank  removed. 

The  regulation  of  feeder  voltage  is 
accomplished  by  turning  the  rotor, 
either  by  hand  or  electrically,  so  as 
to  change  the  relation  of  the  rotor 
winding  to  the  stator  winding.  The 
regulation  is  smooth  and  gradual  in 


FIG.  150. — Westinghouse  sin- 
gle-phase motor  operated  voltage 
regulator. 


either  direction  throughout  the  entire  range  of  the  regulator. 
The  circuit  is  not  opened  at  any  point,  the  effect  of  the 
regulator  being  practically  the  same  as  would  be  obtained  by 
changing  the  generator  voltage. 

The  single-phase  regulator  is  in  effect  a  two-winding  trans- 
former, with  the  secondary  winding  arranged  for  connection  in 


236          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

series  and  the  primary  winding  arranged  for  connection  directly 
across  the  line.  With  a  transformer  thus  connected  a  voltage 
will  be  induced  in  the  secondary  that  will  add  to  or  subtract  from 
the  feeder  voltage  according  to  the  connections  used. 

Action. — With  the  regulator,  the  primary  winding  is  the 
movable  winding  (the  rotor)  and  the  secondary  the  stationary 
winding  (the  stator).  The  current  in  the  primary  produces  a 
magnetic  field  that  induces  a  voltage  in  the  secondary.  The 
portion  of  this  field  passing  through  the  secondary  winding  and 
consequently  the  voltage  induced  in  that  winding,  depends  upon 
the  angular  position  of  the  secondary  with  respect  to  the  direc- 
tion of  the  primary  field.  The  induced  voltage  is  a  maximum 
when  the  axes  of  the  coils  coincide;  zero  when  the  coils  are  at 
right  angles  to  each  other;  and  maximum  in  the  opposite  direc- 
tion when  the  axes  of  the  coils  coincide  but  with  primary  coils 
reversed  in  position.  This  induced  voltage  in  the  secondary, 
therefore,  adds  to  or  subtracts  from  the  feeder  voltage  by  a 
value  varying  from  maximum  regulation  to  zero,  according  to  the 
position  of  the  coils. 

Short-circuited  Winding. — It  is  evident  that  a  magnetic  field 
is  also  set  up  by  the  line  current  flowing  through  the  secondary 
windings  (stator  coils)  which,  if  not  neutralized,  would  produce  a 
choking  effect  and  lower  the  power  factor  in  the  feeder  circuit. 
This  choking  effect  would  occur  whenever  the  primary  winding 
(rotor)  is  in  any  position  other  than  where  the  axes  of  the  two 
windings  coincide — the  positions  of  maximum  "buck"  or 
'"boost" — being  minimum  near  these  positions  and  maximum 
when  the  axes  of  the  two  windings  are  at  right  angles  to  each 
other — the  neutral  positions.  To  overcome  this  choking  effect, 
a  short-circuited  winding  is  placed  in  partially  closed  slots  in  the 
rotor  core  and  at  right  angles  to  the  primary  coils;  this  short- 
circuited  winding  acts  as  a  secondary  to  the  stator  coils  and 
neutralizes  their  choking  effect.  By  using  a  large  number  of 
turns  of  relatively  small  insulated  wire  in  the  short-circuited 
winding,  the  choking  effect  is  neutralized  with  a  comparatively 
small  copper  loss  in  the  short-circuited  winding. 

Polyphase  Regulator. — This  regulator  may  be  likened  some- 
what to  a  phase-wound  polyphase  motor.  The  regulator  pri- 
mary (rotor)  is  wound  with  a  distributed  winding  of  the  same 
number  of  phases  as  there  are  phases  in  the  feeder  to  be  regulated 
and  each  phase  is  connected  across  a  separate  phase  of  the  feeder. 


REGULATORS 


237 


The  regulator  secondary  (stator),  is  made  up  of  separate  wind- 
ings of  the  same  number  as  the  primary,  and  each  of  these  separ- 
ate windings  is  connected  in  series  with  one  of  the  feeder  wires. 

Action. — The  primary  sets  up  a  magnetic  flux  of  constant 
value,  which  induces  a  constant  voltage  in  each  of  the  secondary 
windings.  The  induced  voltage  is  added  therefore  vectorially 
to  the  feeder  as  the  cosine  of  the  angle  between  windings.  As 
the  position  of  the  rotor  is  changed,  the  phase  angles  between  the 
feeder  voltage  and  the  secondary  voltage  correspondingly 
changes,  and  the  feeder  voltage  is  either  increased  or  decreased 
as  the  phase  angle  is  less  or  greater  than  90  degrees. 

Since  the  polyphase  regulator  has  windings  distributed  around 
the  entire  circumference  of  the  rotor,  these  windings  will  also 
act  as  neutralizing  windings  for  the 
various  stator  windings  and  no  sep- 
arate short-circuited  windings,  as  in 
the  case  of  single-phase  regulators,  are 
necessary. 

Motor  Drive. — In  the  standard 
regulators,  the  rotor  is  turned  by  a 
small  alternating-current  induction 
motor  driven  through  a  pinion,  spur 
gear,  worm,  and  worm  segment  (see 
Fig.  151).  The  motor  is  controlled 
non-automatically  by  a  hand  operated 
switch,  or  by  an  electrically  operated 
switch  with  push-button  control 
mounted  in  any  convenient  location; 
or  automatically  by  means  of  relays 
and  other  accessories  especially  made 
for  the  service.  The  motor  operated 
regulators  are  equipped  with  a  hand 
wheel  to  operate  them  by  hand  in  case  of  failure  of  the  control 
circuit. 

A  relay  switch  is  used  to  control  the  motor  circuit  so  as  to 
relieve  the  contacts  of  the  primary  switch  from  the  necessity  of 
carrying  the  current  required  to  operate  the  motor.  On  the 
Westinghouse  regulators  this  relay  switch,  called  the  secondary 
relay,  is  operated  by  a  control  circuit  closed  through  a  hand 
operated  switch  when  non-automatic  operation  is  used,  a  push- 
button switch  generally  being  used — or  through  a  primary  relay 


FIG.  151.  —  Westinghouse 
polyphase  induction  regulator 
motor  operated. 


238         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


when  automatically  operated.     It  is  essentially  an  electrically 
operated  double-pole  double-throw  switch. 

Limit  Switch. — This  is  connected  in  the  operating  circuit 
and  actuated  by  the  operating  mechanism  of  the  regulator, 
prevents  overtravel  of  the  rotor  in  either  direction.  It  is  com- 
bined with  the  secondary  relay  when  that  relay  is  mounted 
on  the  regulator  top-cover;  and  when  the  secondary  relay  is 
mounted  separately  the  limit  switch  is  mounted  directly  on  the 
regulator  top-cover. 

Primary  Relays. — The  voltage  regulating  primary  relay  is  in 
effect  a  voltmeter  having  two  sets  of  contacts  that  control  the 
circuits  operating  the  secondary  relay,  one  circuit  being  closed 
when  the  voltage  rises  above  a  predeter- 
mined value  and  the  other  when  it  falls 
below  another  predetermined  value. 

The  primary  relay  shown  in  Fig.  152  is 
enclosed  in  a  metal  case  with  dustproof 
cover  provided  with  a  window  permitting 
ready  inspection  of  the  operating  parts. 
It  has  compounding  coils  so  that  as  soon 
as  a  change  in  voltage  causes  either  set  of 
contacts  to  close  they  do  not  "chatter" 
but  remain  closed  until  the  voltage  returns 
to  normal.  Means  are  provided  for  ad- 
justing the  relay  for  different  voltage 
variations  and  ranges. 
No-Voltage  Device. — A  special  primary  relay  having  a  no- 
voltage  device  can  be  supplied  to  cause  the  regulator  rotor  to  be 
turned  to  the  position  of  minimum  voltage  in  case  the  power 
supply  in  the  feeder  circuit  is  interrupted.  It,  therefore,  prevents 
the  possibility  of  temporary  overvoltage  on  the  circuit  when  the 
power  supply  is  again  continued.  A  voltage  transformer  of  the 
proper  rating  is  used  to  reduce  the  feeder  voltage  to  a  value  suit- 
able for  the  primary  relay.  A  compensator  is  a  device  connected 
to  the  feeder  circuit  at  the  station  by  means  of  a  current  trans- 
former, and  in  connection  with  a  voltage  transformer,  produces 
at  the  primary  relay  terminals  a  voltage  proportional  to  that  at 
the  distributing  end  of  the  feeder. 

Outdoor  Type  for  Platform  Mounting. — The  outdoor  induct- 
tion  feeder  voltage  regulators  shown  in  Fig.  153  provide  a  means 
of  obtaining  good  voltage  regulation  in  outlying  districts  or  on 


FIG.  152. — Primary 
relay  for  induction 
regulator. 


REGULATORS 


239 


any  other  part  of  an  alternating-current  distribution  system 
without  the  expense  of  housing — they  fit  in  well  with  the  other 
apparatus  now  being  used  so  economically  in  outdoor  substations 
and  other  outdoor  installations. 

Being  entirely  weatherproof  and  self-contained  these  regulators 
may  be  mounted  on  platforms  con- 
structed on  poles  or  on  the  ground, 
protected  by  a  fence  or  screen,  in 
the  same  manner  as  transformers 
in  outdoor  substations.  The  only 
attention  required  is  a  general  in- 
spection for  oiling  the  motor  bear- 
ings and  worm-screw  mechanism, 
filling  grease  cups,  and  examining 
the  relay  contacts  at  regular 
intervals. 

Mounting. — These  regulators  are 
made  for  mounting  on  any  sub- 
stantial flat  surface,  such  as  a 
platform  between  poles  or  on  a 
platform  on  the  ground ;  lifting  lugs 
are  provided  on  the  sides  of  the 
housing  for  raising  the  regulator  to 
the  platform.  As  they  are  not  in- 
tended for  suspension  from  cross- 
arms,  they  are  not  provided  with  FlG.  153._Outdoor  type  induction 

mounting  tugS.  regulator — cover  raised. 

FIELD  RHEOSTATS 

Rheostat. — For  regulating  the  current  in  the  shunt  fields  or 
separately  excited  fields  of  A.C.  and  B.C.  generators  and  motors, 
it  is  customary  to  use  field  rheostats  made  up  of  faceplates  and 
resistors  of  suitable  design.  The  faceplate  comprises  a  series 
of  contacts,  usually  20,  24,  40,  48  or  60,  arranged  in  a  circle 
mounted  on  a  slate  or  marble  base  and  provided  with  a  movable 
contact  arm.  Stops  on  the  faceplate  limit  the  travel  of  the 
contact  arm  which  is  usually  of  the  flat  lever  type  up  to  75 
amperes  and  finger  contact  for  larger,  and  is  mounted  on  a  shaft 
and  operated  either  by  a  handwheel  placed  directly  on  the  shaft 
or  operated  from  a  distance  through  sprocket  and  chain,  bevel 
gears,  solenoids  or  motors.  With  small  A.C.  generators  having 


240         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


their  own  exciters,  concentric  handwheels,  shafts  and  operating 
mechanisms  are  frequently  provided  for  the  generator  and  exciters 
Distant  Control. — There  are  various  advantages  to  be  obtained 
by  mounting  the  rheostat  at  a  distance  from  the  switchboard, 
the  main  ones  being  the  removal  of  the  heat  producing  resistors 
from  the  immediate  neighborhood  of  the  switchboard  and  the 
possibility  of  placing  the  faceplate  close  to  the  resistors.  In 
moderate  capacity  plants,  sprocket-chain  and  wire-rope  trans- 
mission is  customarily  employed  for  connecting  together  the 
handwheel  on  the  switchboard  and  the  faceplate  near 

the  resistors  and  their  re- 
lative location  can  be  made 
to  suit  the  station  require- 
ments. 

In  very  large  stations 
where  electrical  operation 
is  applied  to  the  oil  circuit 
breakers,  the  field  rheostat 
faceplates  are  usually  made 
solenoid  operated  in  the 
smaller  sizes  and  motor 
operated  in  the  larger. 

Solenoid   Control. — Fig. 
154   shows   a    typical    ar- 
rangement   of    a    48-step 
solenoid  operated  faceplate 
mounted  on  grid  resistors. 
The  operating  mechanism 
and  contacts  are  covered 
by  an  iron  shield,  sufficient 
space  being  left  to  allow 
for  inspection,  and  a  hand- 
wheel  being  provided   for 
hand  operation.     The  sol- 
enoid mechanism  consists  of  two  electro  magnets,  a  ratchet  wheel, 
two  pawls,  a  make  and  break  switch  and  the  necessary  levers 
and  springs. 

Motor  Control. — For  larger  capacities  a  motor  operated  face- 
plate, such  as  shown  in  Fig.  155,  is  employed.  This  type  of  face 
plate  is  provided  with  a  clutch  so  that  in  case  of  trouble  to  the 
motor,  the  faceplate  may  be  operated  by  hand,  after  disengaging 


FIG.  154. — Solenoid  operated  field  rheostat. 


REGULATORS 


241 


FIG.  155. — Motor  operated  field  rheostat 
face  plate. 


the  clutch.     With  this  faceplate  a  signal  switch  is  provided  to 

light  up  a  lamp  on  the  switchboard  when  the  contact   arm  is 

bridging  two  contacts.     This  faceplate  is  also  provided  wi'th 

limit  switches  that  open  up 

the  control  circuit  when  the 

contact  arm  has  reached  the 

limit  of  its  travel  in  either 

direction.     The  connections 

are  so  made  that  while  the 

rheostat  can    no  longer  be 

operated  in  one  direction  it 

can  be  operated  in  the  other. 

Resistors. — Modern  rheo- 
stat resistors  are  usually 
either  of  the  bar  form  or  the 
grid  form.  The  bar  form 
consists  essentially  of  an 
iron  bar  covered  with  a 
suitable  insulation  and 
wound  over  with  a  wire  of 
varying  sizes  so  that  with  a 

bar  1  inch  by  ^  inch  in  section,  the  resistance  per  linear  inch  of 
bar  can  be  varied  from  0.03  to  400  ohms,  with  a  maximum 
capacity  of  4  watts  per  linear  inch. 

Grids. — For  heavier  capacities  grid  resistors  are  employed, 
these  being  made  of  cast  iron  of  considerable  mechanical  strength 
and  high  thermal  capacity.  These  grids  are  cast  in  various  shapes 
to  secure  the  desired  resistance  and  are  assembled  on  insulated 
rods  and  clamped  together,  being  connected  in  series  or  multiple 
as  required. 

GENERATOR  REGULATORS 

Generator  Regulation. — The  earliest  plants  with  poorly  regula- 
ting generators  were  only  able  to  maintain  proper  voltage  by 
depending  on  the  switchboard  operator  to  continually  adjust  the 
voltage  by  means  of  the  rheostat.  To  reduce  the  amount  of 
adjusting,  generators  were  made  with  very  good  inherent  regula- 
tion and  various  schemes  were  developed  to  get  the  equivalent 
of  a  compound  winding  on  an  A.C.  generator.  These  generators 
with  close  inherent  regulation  were  expensive  to  build  and  their 
windings  were  difficult  to  brace  against  the  effects  of  short  cir- 

16 


242         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

cults  so  the  trend  of  generator  design  turned  to  generators  with 
high  reactance  and  poor  inherent  regulation,  as  soon  as  a  satis- 
factory regulator  had  been  developed  for  maintaining  the  A.C. 
voltage  at  its  proper  value  under  conditions  of  varying  load. 

Tirrill  Regulators. — In  order  to  maintain  practically  constant 
voltage  on  A.C.  and  D.C.  generators,  or  to  have  those  machines 
compound  automatically  to  take  care  of  feeder  drop,  field  regu- 
lators of  various  kinds  have  been  designed,  the  best  known  being 
the  Tirrill. 

While  Mr.  Tirrill  has  been  connected  at  one  time  with  the  Gen- 
eral Electric  Company  and  later  with  the  Westinghouse  Electric  & 
Manufacturing  Company  working  on  regulator  designs,  he  has 
not  been  with  either  company  for  a  number  of  years,  and  many 
of  the  features  of  the  regulators  were  due  to  the  ideas  of  other 
engineers  at  these  two  companies.  His  name  has  been  so  closely 
connected  with  the  development  of  this  type  of  voltage  regula- 
tors that  most  engineers  not  connected  with  the  two  manufac- 
turing companies  are  still  apt  to  speak  of  the  regulators  as  a 
"G.  E.  Tirrill"  or  a  "Westinghouse  Tirrill"  although  neither 
company  uses  the  name  "Tirrill"  in  describing  their  regulators. 

A.C.  Regulators. — The  various  uses  to  which  alternating-cur- 
rent voltage  regulators  are  best  adapted  fall  into  the  following 
divisions :  (a)  the  maintenance  of  constant  voltage  at  generator, 
bus,  or  some  predetermined  center  of  distribution;  (6)  the  main- 
tenance of  constant  voltage  at  the  end  of  transmission  lines  by 
the  control  of  synchronous  condensers  or  synchronous  boosters; 
(c)  the  control  of  booster-type  rotaries;  (d)  the  control  by  special 
regulators  of  synchronous  condensers  applied  to  local  network 
or  distributing  systems  for  voltage  regulation  and  power  factor 
correction;  and  (e)  the  maintenance  of  constant  current  instead 
of  constant  voltage. 

D.C.  Regulator — G.  E.  Type. — For  direct-current  service 
the  G.  E.  regulator  consists  essentially  of  a  main  control  magnet 
with  two  independent  windings  and  a  differentially  wound  relay 
magnet  with  connections  about  as  shown  in  Fig.  156.  The 
potential  winding  of  the  main  control  magnet  is  connected  across 
the  generator  terminals  and  the  other  winding  across  a  shunt  in 
one  of  the  load  mains.  This  opposes  the  action  of  the  potential 
winding  and  makes  the  generator  over  compound  for  line  drop. 
The  main  features  of  the  diagram  are  self  evident.  When  the 
effect  of  the  potential  winding  diminishes,  due  to  drop  in  volt- 


REGULATORS 

*•»*«•* 


243 


«««*«•        •**•+»*•••.: 

TO- if 5     /OS    /JO     I/S     /20   IZS 

ra-sjo    sso 
FIG.  156. — G.  E.  voltage  regulator  for  D.C.  machines. 


Current 
Transformer 


FIG.  157. — G.  E.  voltage  regulator  for  A.C.  machines. 


244         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

age  or  increase  in  load,  the  spring  lifts  the  main  contact  which 
in  turn  energizes  the  relay  magnet  closing  the  relay  contact,  thus 
short-circuiting  the  generator  rheostat  and  raising  the  voltage. 
The  relay  contacts  are  shunted  by  a  condenser  to  reduce  the 
sparking. 

A.C.  Regulator — G.  E.  Type. — With  A.C.  generators,  that  are 
almost  invariably  separately  excited,  the  G.  E.  regulator  works 
on  the  exciter  field  as  shown  in  the  simplified  diagram  of  con- 
nections in  Fig.  157.  The  main  contacts  with  this  type  of  regula- 
tor are  acted  on  by  two  sets  of  control  magnets,  one  connected 
across  the  exciter  bus  and  tending  to  move  the  main  contacts 
further  apart  as  the  exciter  voltage  rises  while  the  other  control 
magnet  is  acted  on  by  an  A.C.  potential  coil  and  current  coil 
while  suitable  springs  and  counter  weights  allow  the  proper  ad- 
justments to  be  made.  When  the  main  contact  closes  it  energizes 
the  relay  magnet,  closing  the  relay  contact,  short-circuiting  the 
exciter  rheostat  and  raising  the  exciter  voltage  and  consequently 
the  generator  voltage. 

Compensation. — As  may  be  noticed  from  the  diagram  the  com- 
pensating winding  is  provided  with  a  dial  switch  to  give  any 
amount  of  compensation  required  for  the  feeder  circuit  in  which 
the  current  transformer  is  located.  Where  it  is  desired  to  com- 
pensate for  both  ohmic  and  inductive  drop  under  varying  power 
factors  a  special  compensator  is  provided.  A  modification  of  the 
regulator  to  take  care  of  larger  exciters  has  a  plurality  of  relay  con- 
tacts, all  operated  at  the  same  time  from  the  one  set  of  control 
contacts,  the  various  relay  contacts  being  shunted  by  condensers 
to  reduce  the  sparking. 

D.C.  Control. — The  features  of  the  G.  E.  regulator,  that  have 
been  so  conducive  to  its  successful  operation,  are  the  method  of 
control  adopted  and  the  fact  that  with  the  total  range  of  regu- 
lation from  no-load  to  full-load  the  maximum  travel  of  the  only 
moving  parts,  the  vibrating  contacts,  is  only  3^2  inch.  The 
vibrations  are  so  rapid  that  the  time  factor  is  reduced  to  the  mini- 
mum possible  limit  and  there  are  no  retarding  effects  due  to  dash- 
pots  or  other  damping  devices.  The  use  of  the  exciter  voltage 
as  one  of  the  main  control  circuits  also  prevents  overshooting  for, 
as  the  exciter  voltage  rises  to  bring  up  the  A.C.  voltage,  the  D.C. 
control  tends  to  keep  the  main  contacts  apart  and  so  reduce  the 
voltage  again. 


REGULATORS 


245 


Westinghouse. — Westinghouse  voltage  regulators,  arranged 
in  a  suitable  case,  are  constructed  for  bracket,  panel,  or  pedestal 
mounting,  as  required  by  installation  conditions.  Bracket 
mounted  regulators  are  provided  with  a  standard  black-marine 
slate  base. 

The  regulator  parts  as  shown  in  Fig.  158  are  arranged  in  the 
case  with  the  control  system  located  in  the  upper  part  supported 
on  a  small  cast  base,  and  with 
the  rheostat  shunting  relays  ar- 
ranged in  horizontal  rows  at  the 
bottom.  The  control  element 
and  relays  are  self-contained 
units  and  either  may  be  re- 
moved from  the  base  without 
disturbing  its  adjustment. 

Control. — The  control  system 
for  alternating-current  and  sep- 
arately excited  direct-current 
generators  consists  of  the  main 
control  magnet  and  the  vi- 
brating magnet,  with  the  main 
contacts  between  them.  The 
magnets  are  of  the  solenoid 
type,  and  are  very  sensitive. 
They  are  provided  with  ad- 
justable dashpots  to  permit 
adjustment  of  regulation  to 
suit  the  characteristics  of  the 
system. 

Vibrating  Relay. — One  of  the  relays,  called  the  vibrating 
magnet  relay,  is  used  to  govern  the  operation  of  the  vibrating 
magnet.  On  the  larger  size  generators,  one  or  more  master 
relays  are  used  to  control  a  group  of  rheostat  shunting  relays, 
thus  relieving  the  main  contacts  of  handling  control  circuits 
beyond  their  capacity. 

Master  Relay. — The  use  of  the  master  relay  is  made  possible 
by  the  alternating-current  control  and  permits  of  the  construction 
of  regulators  with  as  many  as  60-rheostat  shunting  relays.  The 
master  relay  introduces  no  time  lag  in  the  response  of  the  regu- 
lator, nor  in  the  voltage  regulation,  since  the  vibrating  magnet 
relay  and  the  rheostat  shunting  relays  operate  simultaneously. 


FIG.    158. — Wcstinghouso    automatic 
generator  voltage  regulator. 


246         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


Action.— Referring  to  Fig.  159  the  main  control  magnet  has 
its  core  attracted  upward.  Its  core  stem  is  connected  to  the 
floating  lever,  which  is  pivoted  to  the  bell-crank  lever  of  the 
vibrating  magnet.  A  counterweight  is  used  to  assist  the  pull 
of  the  main  control  magnet,  and  to  bring  the  lever  and  core  to 
a  balanced  position  at  the  normal  voltage  to  be  regulated.  The 
vibrating  magnet  also  has  its  core  attracted  upward.  Its  core 
stem  is  connected  to  one  end  of  the  bell-crank  lever  which  is 
pivoted  to  the  base,  and  its  opposite  end  carries  the  floating 
lever  of  the  main  control  magnet.  The  pull  of  this  vibrating 


Main  Contacts 
Main  Control 


Pivot 


'Voltage  Limiting  Rheostat  V.  C  Field  Rheostat 

FIG.   159. — Westinghouse  voltage  regulator  diagram. 

magnet  is  assisted  by  a  single  spring  as  shown.  These  two  mag- 
nets are  energized  from  the  same  voltage  transformer,  and  actuate 
the  movable  main  contact  into  and  out  of  engagement  with  the 
fixed  contact. 

Diagram. — An  inspection  of  the  schematic  diagram  shows 
that  the  closure  of  the  main  contacts  causes  all  relay  contacts 
to  close.  One  of  the  relays,  called  the  vibrating  relay,  is  con- 
nected so  that  the  closure  of  its  contacts  shunts  a  small  portion 
of  the  resistance  in  series  with  the  vibrating  magnet,  thus  increas- 
ing its  pull  and  opening  the  main  contacts.  The  opening  of 
the  main  contacts  open  all  relay  contacts  and  inserts  the  full 
resistance  in  the  vibrating  magnet  circuit,  weakening  the  pull 
and  closing  the  main  contacts  again. 

From  the  above  cycle,  it  is  seen  that  for  any  given  position 
of  the  floating  lever,  a  condition  of  continuous  vibration  results. 


REGULATORS  247 

A  necessary  condition  to  the  continuous  vibration  of  the  system 
is  that  the  weight  of  the  vibrating  magnet  core  and  lever  must  be 
exactly  balanced  by  the  tension  of  the  control  spring  and  average 
pull  of  the  magnet.  Any  change  in  the  tension  of  the  control 
spring  results  in  an  equal  change  in  the  average  magnet  pull. 
For  a  given  line  voltage  there  is  a  definite  magnet  pull  when 
the  contacts  are  closed,  and  a  definite  pull  of  less  value  when 
the  contacts  are  opened.  The  average  magnet  pull  must  be  a 
function  of  the  time  of  the  contact  engagement.  For  any  given 
position  of  the  floating  lever,  there  is  a  corresponding  position 
of  the  bell-crank  lever  and  tension  of  the  control  spring.  How- 
ever, on  account  of  the  balanced  condition  there  must  be  a 
corresponding  average  magnet  pull  and  time  of  contact  engage- 
ment. 

Rheostat  Shunting  Relays. — The  contacts  of  these  relays 
open  and  close  across  the  shunt  field  rheostat  of  the  exciter,  and 
the  effective  resistance  of  the  rheostat  is  determined  by  the  time 
of  contact  engagement.  For  any  effective  resistance,  there  is 
a  corresponding  exciter  voltage,  and,  therefore,  A.C.  voltage. 

A.C.  Control. — As  the  control  element  is  energized  from  the 
A.C.  generator  the  main  control  magnet  will  assume  a  position 
such  that  a  time  of  contact  engagement  is  maintained  sufficient 
to  develop  an  exciter  voltage  and,  therefore,  an  A.C.  voltage 
capable  of  balancing  the  core  weight.  Any  variation  in  line 
voltage  changes  the  position  of  the  floating  lever  in  such  a 
manner  as  to  vary  the  excitation  and  restore  the  balance. 

There  are  many  interesting  features  such  as  the  equalizing 
rheostats  used  with  two  or  more  exciters,  the  overvoltage 
relays  to  guard  against  trouble  from  excessive  rise  of  voltage 
if  a  contact  should  stick  which  cannot  be  more  than  mentioned 
in  this  place. 

For  further  details  regarding  the  methods  of  operation,  the 
cutting  of  the  regulator  into  and  out  of  service,  the  securing 
of  line  drop  compensation,  the  parallel  operation  of  voltage 
regulators,  reference  should  be  had  to  the  manufacturers'  cata- 
logues, instruction  books  and  similar  publications. 

Application. — The  successful  application  of  voltage  regulators 
depends  on  several  factors  entirely  independent  of  the  size  and 
design  of  the  regulator  itself.  It  is  not  only  necessary  that  the 
regulator  be  properly  designed,  but  it  is  also  essential  that  the 
exciters,  generators,  and  prime  movers  possess  characteristics 


248         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

that  will  harmonize  with  each  other  and  will  assist  in  keeping  the 
voltage  at  the  desired  value  under  rapidly  changing  load  condi- 
tions. In  general,  the  following  conditions  should  be  approached 
as  nearly  as  possible  in  order  to  obtain  satisfactory  reults : 

1.  Prime  movers  must  be  provided  with  proper  automatic 
governors  that  will  respond  instantly  to  changes  in  load  and  keep 
the  speed  reasonably  constant  (within  3  percent  to  4  percent 
from  no-load  to  full-load). 

2.  Alternating-current  generators  should  have  as  nearly  as 
possible  the  same  percentage  range  of  excitation  from  no-load  to 
full-load. 

3.  Exciters  must  be  capable  of  delivering  sufficient  voltage  to 
take  care  of  the  alternating  current  generator  fields  under  full- 
load  conditions,  80  per  cent,  power  factor,  plus  a  certain  additional 
voltage.     This  additional  voltage  above  the  steady  exciter  volt- 
age required  to  maintain  constant  bus  voltage  under  full-load  con- 
ditions, is  necessary  in  order  that  the  regulator  will  continue  to 
vibrate  and  thereby  have  control  of  the  exciter. 

4.  Exciters    (where   more   than   one   are   to   be   considered) 
must  be  adjusted  to  operate  in  parallel  under  all  loads  and  at  any 
point  of  the  saturation  curve. 

5.  Exciters  for  125-volt  service  should  be  able  to  build  their 
voltage  up  or  down  between  the  limits  of  30  and  125  volts  in  5 
seconds  or  less  under  load  consisting  of  generator  field  circuits. 
The  time  constant  should  be  the  same  for  exciters  of  other  rated 
voltages  over  proportional  ranges.     Exciters  with  greater  time 
constants  than  this  may  not  permit  the  regulator  to  maintain 
constant  voltage  with  rapidly  fluctuating  load. 

6.  125-volt  interpole  exciters  must  be  able  to  develop  at  least 
135  volts  with  the  series  winding  disconnected,  and  should  be  so 
operated.     The  series  winding  must  be  cut  out  of  circuit  in  order 
to  secure  a  satisfactory  time  constant.     In  general,  the  exciter 
must  be  capable  of  developing  a  voltage  10  to  15  per  cent,  in 
excess  of  that  required  by  the  A.C.  generator  at  full-load,  80 
per  cent,  power  factor,  the  A.C.  generator  field  rheostat  being 
adjusted  so  that  with  60  volts  on  a  125-volt  exciter  the  A.C. 
generator  develops  normal  voltage  at  no-load. 

Flicker. — On  small  systems,  supplying  a  mixed  lighting-and- 
power  load,  where  induction  motors  are  sometimes  thrown  direct- 
ly on  the  line  without  starting  devices,  the  momentary  current 
required  may  be  of  such  a  value  as  to  affect  the  feeder  system  and 


REGULATORS  249 

cause  a  noticeable  flicker  in  the  lights.  Automatic  regulating 
devices  in  the  generating  station  cannot  be  made  sensitive  enough 
to  prevent  this  effect  under  such  conditions. 

Voltage  Adjusting  Rheostats. — Taps  are  always  provided 
on  the  external  resistor  whereby  the  voltage  regulated  can  be 
varied  from  104  volts  •  secondary  to  116,  in  steps  of  6  volts. 
Where,  for  any  reason  it  is  desired  to  vary  the  operating  voltage 
of  the  system  from  time  to  time,  a  voltage  adjusting  rheostat 
should  be  used  in  the  control  element  circuits  for  the  fine  adjust- 
ment of  voltage,  instead  of  varying  the  counterweight.  This 
rheostat  has  a  sufficient  resistance  to  give  an  adjustment 
of  about  6  volts  either  way  from  the  normal  voltage  when  properly 
applied.  The  use  of  this  rheostat  is  recommended  in  all  applica- 
tions, as  it  is  a  much  more  convenient  and  satisfactory  method  of 
adjusting  the  voltage  while  the  regulator  is  in  operation. 

Single  Operation  of  Exciters  and  Parallel  Operation  of  Gen- 
erators.'— By  the  use  of  a  control  element  energized  entirely 
from  the  A.C.  system,  the  operation  of  alternating-current  gen- 
erators in  parallel  with  the  exciters  operating  singly,  has  been 
made  possible.  The  regulators  for  such  service  are  equip- 
ped with  special  transfer  switches  so  that  the  D.C.  circuit  for 
energizing  the  relays  may  be  transferred  to  any  exciter  that 
may  be  in  operation. 

Compensation. — For  complete  line  drop  compensation,  it  is 
necessary  to  consider  two  factors,  namely,  inductive  drop  and 
ohmic  drop  in  the  line  and  transformers  between  the  generator 
bus  and  the  distributing  center.  The  inductive  component  of 
line  drop  is  at  right  angles  to  the  load  current  and  is  compensated 
for  by  introducing  into  the  potential  circuits  of  the  regulator  a 
voltage  in  phase  with  and  proportional  to  the  actual  inductive 
drop.  An  external  compensator,  energized  from  series  trans- 
formers, properly  connected,  accomplishes  this  purpose.  This 
compensator  is  provided  with  adjustable  dials  by  means  of  which 
the  voltage  introduced  in  the  regulator  circuits,  for  a  given  am- 
pere load,  may  be  varied,  thus  permitting  adjustment  for  the 
percentage  inductive  load. 

The  ohmic  component  of  line  drop  is  in  phase  with  the  load 
current  and  is  compensated  for  by  energizing  the  current 
windings  of  the  regulator  coils  from  series  transformers  properly 
connected.  The  regulator  control  magnets  are  then  affected 
by  a  magnetizing  force  which  is  in  phase  with  the  load  current. 


250         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

The  current  windings  on  the  regulator  coils  are  divided  into  sec- 
tions and  connected  to  an  adjustable  dial.  This  provides  a 
ready  means  of  obtaining  the  proper  percentage  of  ohmic  com- 
pensation. Fig.  160  shows  the  connections  to  3-phase  systems 
for  this  method. 


Direction  ot Power  -••• 


The  obovt  connections  are  correct  'or  a  secondary  operating  voltage  of  HO  Volts  II  a  HI- 
ferent  operating  vo"o<jf  is  required,  refer  to  the  diagram  of  connections  fumistno'  with 
the  Vol'oge  Aft  lusting  ffheostol  'or  the  proper  connections  to  tn*  C'ltrngl  ren'stor 

FIG.  160. — Compensator  connections  for  regulator. 

To  obtain  complete  line  drop  compensation  it  is  necessary  to 
adjust  both  the  compensating  devices  to  agree  with  the  line  char- 
acteristics. Where  ohmic  line  drop  compensation  only  is  desired 
no  external  compensator  is  necessary.  The  current  windings  on 
the  regulator  coils,  when  properly  energized  from  series  trans- 
formers, accomplish  this  result.  For  3-phase  systems,  two 
current  transformers  in  vector  parallel  are  required  for  complete 
compensation.  The  transformers  must  be  in  the  same  legs  of  the 
circuit  as  those  to  which  the  voltage  transformer  is  connected  in 
order  that  the  resultant  current  will  be  in  phase  with  the  voltage 
at  100  per  cent,  power  factor. 

Parallel  Stations. — Where  stations  operate  in  parallel,  and  each 
is  controlled  by  a  voltage  regulator,  it  is  possible  to  compensate 
for  the  ohmic  drop  only,  as  inductive  compensation  destroys  the 
stability  of  the  system.  The  point  in  the  system  at  which  it  is 
desired  to  maintain  constant  voltage  should  be  determined 
in  order  to  obtain  proper  compensation. 

Condensers. — These  are  required  for  connection  across  the 
rheostat  shunting  relays,  to  minimize  the  contact  wear  occa- 
sioned by  the  sparking  incident  to  the  opening  of  the  shunt  across 
the  exciter  field  rheostats. 


REGULATORS  251 

Exciter  Rheostats. — When  a  regulator  equipment  is  being 
added  to  a  plant  in  operation,  the  existing  exciter  rheostats  should 
be  checked  to  determine  whether  they  have  sufficient  resistance 
to  permit  of  adjusting  the  exciter  for  the  proper  time  constant. 
If  not,  new  exciter  rheostats  must  be  provided.  If  the  shunt 
field  rheostat  of  the  exciter  used  for  hand  control  is  unsuitable  for 
use  with  the  regulator,  it  can  in  many  cases  be  used  as  the  voltage- 
limiting  rheostat. 

Auxiliary  Exciter  Rheostats. — Where  two  or  more  exciters, 
operating  either  singly  or  in  parallel,  are  controlled  from  a 
regulator,  the  use  of  an  auxiliary  rheostat  is  required  in  the  field 
circuits  of  each  exciter  to  adjust  the  time  constants  and  maxi- 
mum voltage  of  all  the  exciters  to  the  same  values  in  order  that 
they  will  carry  their  proper  share  of  load.  Where  only  one 
exciter  is  controlled  by  a  regulator  the  use  of  an  auxiliary  rheostat 
is  not  required  unless  too  high  a  maximum  voltage  and,  conse- 
quently, too  large  a  field  current,  is  obtained  when  the  main 
exciter  rheostat  is  short-circuited  by  the  relay  contacts. 

Voltage  Transformers. — These  of  400  volt  ampere  capacity 
with  fuse  blocks  and  fuses  are  required  for  all  alternating-cur- 
rent voltage  regulators. 

Current  Transformers  are  required  only  when  compensation 
for  line  drop  in  some  particular  circuit  is  desired,  or  when  two  or 
more  regulators  are  operating  in  parallel.  One  current  trans- 
former is  required  for  partial  compensation  or  two  for  full  com- 
pensation, and  one  transformer  is  necessary  for  each  regulator 
where  two  or  more  regulators  operate  in  parallel.  No  current 
transformer  is  necessary  when  it  is  desired  to  maintain  constant 
bus  voltage. 

Voltage  Rise. — With  the  ordinary  type  of  generator  voltage 
regulator,  when  a  short  circuit  on  a  system  is  cleared  away,  a 
dangerous  voltage  rise  is  inevitable.  On  the  occurrence  of  a 
short  circuit  on  a  system  without  some  protective  device,  the 
main  contacts  of  the  regulator  close,  causing  the  relay  contacts  to 
close  and  the  exciter  voltage  to  build  up  to  the  maximum  value. 
When  the  short  is  cleared  away,  a  high  voltage  results,  due  to  the 
high  exciter  voltage  and  consequent  high  generator  field  current, 
which  lasts  until  the  regulator  has  had  time  to  again  become 
operative. 

Excess  Voltage  Device. — This  condition  of  excessive  voltage 
can  be  prevented  by  means  of  the  excess  voltage  protective 


252         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

device,  which  can  be  applied  to  any  Westinghouse  A.C.  regulator. 
A  diagrammatic  view  of  this  device  is  shown  in  Fig.  161.  It 
consists  of  an  undervoltage  relay  in  combination  with  a  direct- 
current  control  element  connected  in  the  main  contact  circuit  of 
the  alternating-current  voltage  regulator.  The  contacts  of  the 
D.C.  element  and  the  relay  are  connected  in  parallel,  the  pair 
being  in  series  with  the  main  contacts  of  the  regulator.  The 
D.C.  element  is  energized  from  the  exciter  bus,  and  the  relay 
from  the  potential  transformer  supplying  the  A.C.  regulator. 


Main  Contacts  of  Regulator 


FIG.   161. — Excess  voltage  protection  for  regulator. 


A  short  circuit  coming  on  a  system  equipped  with  this  protec- 
tive device  immediately  causes  the  main  contacts  of  the  regulator 
to  close  and  the  A.C.  relay  contacts  to  open,  on  account  of  the 
drop  in  the  A.C.  voltage.  As  soon  as  the  exciter  voltage  builds 
up  to  the  point  for  which  the  D.C.  element  is  adjusted,  the  con- 
tacts of  this  element  begin  to  operate  and  to  regulate  the  exciter 
voltage  in  the  same  manner  that  the  regulator  contacts  normally 
do,  so  that  the  exciter  voltage  can  never  rise  above  the  predeter- 
mined point,  which  is  usually  a  little  above  the  no-load  excitation 
value  required  by  the  A.C.  generators.  When  the  short  circuit 
is  relieved,  therefore,  no  excessive  field  current  exists  to  produce 
a  dangerous  rise  in  A.C.  voltage.  The  moment  the  A.C.  voltage 
rises  above  the  setting  of  the  undervoltage  relay,  the  contacts 
of  the  relay  close  and  put  the  A.C.  voltage  regulator  back  into 
service. 

Battery  Control. — Where  storage  batteries  are  used  in  a  power 
plant  it  is  ordinarily  necessary  to  provide  some  means  of  keeping 
a  fairly  constant  voltage  on  the  D.C.,  bus  bars  or  constant 


REGULATORS  253 

load  on  the  generators  independent  of  the  condition  of  charge  of 
the  battery  or  load  on  the  feeder  circuits.  As  the  usual  lead  cell 
when  fully  charged  has  a  voltage  of  2.5  per  cell  and  as  it  is  safe  to 
discharge  a  battery  down  to  about  1.75  volts  per  cell  it  is  evident 
that  some  means  must  be  provided  to  take  care  of  this  range  of 
voltage. 

While  end  cell  switches  are  used  to  a  certain  extent,  the  end 
cells  are  only  in  service  part  of  the  time  and  do  not  get  the  same 
service  as  the  rest  of  the  battery.  In  order  to  work  all  of  the 
cells  the  same  amount  it  is  customary  to  install  a  booster  whose 
voltage  added  to  or  taken  from  that  of  the  battery  will  give  the 
desired  pressure  on  the  bus  bars.  Without  going  deeply  into 
the  design  of  the  battery  or  the  booster  it  may  suffice  to  say  that 
boosters  usually  have  their  armatures  connected  in  series  with 
the  battery  across  the  bus  while  the  field  circuit  on  the  booster 
may  be  series,  shunt  or  separately  excited. 

In  order  to  avoid  the  necessity  of  hand  regulation  of  the  booster 
voltage  many  very  ingenious  regulating  schemes  have  been 
devised  and  regulators  make  these  schemes  effective  and  enable 
the  voltage  of  the  booster  to  automatically  change  in  direction 
and  amount  so  as  to  enable  the  battery  to  charge,  discharge  or 
float  on  the  line. 


CHAPTER  X 
INDUSTRIAL  CONTROL  APPARATUS 

While  it  is  not  the  intention  of  this  book  to  go  deeply  into  the 
question  of  industrial  control  apparatus  these  devices  are  so 
frequently  used  in  connection  with  other  switching  equipment  for 
the  control  of  the  automatic  substations  or  of  motors  in  a  power 
plant  that  it  is  necessary  to  give  some  short  descriptions  of  some 
of  the  devices  most  frequently  used  in  connection  with  the  other 
switch  gear  devices. 

It  is  difficult  to  draw  a  very  definite  line  in  some  cases  between 
control  apparatus  and  switching  equipment  for  power  control 
but  the  former  may  be  considered  primarily  as  intended  for 
motor  control  while  the  latter  is  used  for  power  plants  and  general 
distribution.  Control  apparatus  is  designed  for  severe  service 
and  very  adverse  conditions  and  ruggedness  is  its  essential 
characteristic,  with  appearance  considered  usually  of  minor 
importance. 

Apparatus. — Some  of  the  devices  such  as  contactors,  controllers, 
starters,  etc.  will  be  considered  in  a  rather  brief  fashion  as  a 
full  discussion  would  go  beyond  the  province  of  this  book  and 
should  be  reserved  for  a  book  dealing  particularly  with  that 
subject. 

Contactors. — Contactor  switches  or  contactors  might  be  de- 
scribed as  switches  or  circuit  breakers  requiring  some  auxiliary 
source  of  power,  such  as  a  solenoid  or  compressed  air  to  hold 
them  in  the  closed  position.  They  are  used  principally  for 
motor  control  and  are  designed  primarily  for  multiple  unit 
control  of  railway  motors  and  automatic  or  semi-automatic 
control  of  industrial  motors.  These  contactors  are  made  in 
many  forms  by  different  companies  and  except  for  the  electro- 
pneumatic  system  of  multiple  unit  train  control  are  usually 
made  solenoid  operated  and  frequently  provided  with  magnetic 
blowout  attachments. 

254 


INDUSTRIAL  CONTROL  APPARATUS 


255 


FIG.    162.  —  Con- 
tactor switch. 


Typical  Design. — In  the  design  illustrated  in  Fig.  162  the 
contactors  are  built  in  sizes  up  to  1250  amperes  D.C.  and  they 
consist  essentially  of  a  contact  that  is  closed  by  the  action  of  a 
solenoid  which  raises  its  plunger  vertically  when  the  coil  is 
energized  and  allows  it  to  drop  back  by  gravity 
assisted  by  springs  when  the  coil  is  de- 
energized.  The  main  contacts  are  above  the 
solenoid  and  are  protected  by  magnetic 
blowout  coils  which  are  so  placed  on  each 
side  of  the  main  contact  that  the  arc  is  forced 
quickly  to  the  front  and  blown  out.  In 
this  design  the  main  contacts  are  of  the  butt 
type,  the  lower  portion  being  moved  by  the 
plunger  and  the  upper  portion  being  fixed 
either  rigidly  or  with  a  slight  spring  motion. 
The  main  contacts  in  the  larger  sizes  are 
double,  the  arcing  tips  being  made  of  brass 
and  being  readily  renewable  and  the  other  contacts  being  of 
copper. 

Interlock  Contacts. — These  contacts  located  below  the  solenoids 
consist  of  flat  brass  discs  carried  on  an  insulating  rod  attached 
to  the  lower  end  of  the  plunger  rod,  these  rings  making  contact 
against  copper  blocks  attached  at  the  outer  ends  of  insulating 
supports  hung  down  from  the  contactor.  These  interlocking  con- 
tacts carry  only  the  small  amount  of  current  required  for  the 
magnet  coil.  These  contacts  can  be  readily  arranged  to  secure 
practically  any  scheme  of  electrical  interlocking  that  may  be 
desired  and  to  insure  the  closing  of  a  series  of  contactors  in  any 
predetermined  sequence. 

Master  Switch. — These  contactors  are  ordinarily  used  in 
connection  with  a  master  switch  or  controller  and  protective 
relay  switches  of  various  kinds  to  insure  the  performance  of  vari- 
ous functions,  such  as  the  automatic  cutting  in  and  out  of 
resistance  in  the  secondary  of  an  induction  motor;  to  maintain 
constant  input  to  a  flywheel  set;  or  any  similar  features  that  may 
be  desired. 

Controller. — A  controller  may  be  described  as  a  switching 
device,  usually  with  a  movable  arm  or  drum,  that  makes  various 
connections  in  a  predetermined  manner  for  the  purpose  of  starting 
one  or  more  motors  and  regulating  their  speed,  output  or  other 
characteristics. 


256         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Functions. — Controllers  are  designed  to  be  used  with  motors  of 
different  kinds  and  to  take  care  of  the  functions  not  incorporated 
in  the  motor  design  in  order  to  enable  the  latter  to  operate  under 
the  specified  conditions  of  load.  The  functions  usually  sup- 
plied by  the  controllers  are  the  following: 

To  limit  the  current  during  the  acceleration  of  the  motor. 
To  limit  the  torque  during  acceleration. 
To  change  the  direction  of  rotation  of  the  motor. 
To  limit  the  load  on  the  motor. 
To  disconnect  the  motor  on  failure  of  voltage. 
To  regulate  the  speed  of  rotation. 

To  start  and  stop  the  motor  at  fixed  points,  on  the  cycle  of  operation,  or 
at  the  limit  of  travel  of  the  load. 
To  stop  the  motor. 
To  protect  the  operator  from  injury. 

Not  every  controller  has  to  embody  all  of  these  features  in  the 
same  degree  but  these  are  the  underlying  points  of  controller 
design  and  they  must  be  procurable  when  they  are  needed. 

Faceplate  Controller. — The  simplest  form  of  controller  for 
starting  and  regulating  the  speed  of  the  D.C.  motor  is  the  face- 
plate type  shown  diagrammatically  in  Fig.  163,  and  intended  for 
use  with  a  variable  speed  motor  connecting  resistors  in  the  arma- 
ture and  field  circuit.  With  this  type  of  controller  the  contacts 
are  mounted  on  the  face  of  a  suitable  slab  and  a  moving  arm 
makes  the  connections  to  the  armature  and  field  circuits,  the 
speed  of  the  motor  being  changed  by  varying  the  field  strength. 
The  rheostat  arm  is  made  in  two  parts,  the  under  part  making 
contact  with  the  segment  of  R-l  to  R-12  and  with  the  contact 
ring  E,  while  the  top  arm  engages  the  upper  row  of  round  contacts. 
When  starting,  the  two  arms  are  held  together  by  a  latch.  The 
bottom  arm  is  provided  with  a  notched  segment  engaging 
the  plunger  forming  part  of  the  low  voltage  release  magnet.  The 
notch  segment  and  pawl  hold  the  arm  in  any  operating  position 
after  the  low  voltage  magnet  is  energized.  To  start  the  motor  the 
contact  arms  are  moved  from  the  off  position  to  contact  R-l 
and  the  connections  can  readily  be  traced  from  that  point.  The 
arms  are  gradually  moved  to  the  right  eliminating  successively 
each  section  of  the  armature  resistor  until  the  bottom  arm  makes 
contact  with  R-12.  In  this  position  the  armature  is  connected 
directly  across  the  lines  and  the  segment  E  disconnected  from 
the  rheostat  arm.  The  shunt  field  circuit  now  is  from  the  posi- 


INDUSTRIAL  CONTROL  APPARATUS 


257 


live  side  of  the  line  to  the  upper  rheostat  arm  to  the  right  hand 
field  contact  F-12,  thence  to  the  field  winding.  This  gives  a 
motor  speed  due  to  full  field  strength.  If  it  is  desired  to  increase 
the  speed  of  the  motor  the  upper  arm  can  be  moved  to  the  left 
across  the  field  contacts  to  insert  resistance  gradually  in  the  shunt 
field  circuit,  and  thus,  within  its  range,  give  the  increased  speed 
desired,  while  the  low  voltage  release  magnet  holds  the  lower 


Armature  Regulating 
Beiiitor 


Field  Regulating 
Eeiistor 


L- 


FIQ.   163. — Face  plate  controller. 


arm  on  contact  R-12.  If  the  circuit  is  interrupted  the  low  voltage 
release  magnet  will  allow  the  lower  arm  to  be  carried  to  the  off 
position  by  means  of  a  spring.  This  in  turn  picks  up  the  upper 
arm  and  the  two  are  moved  quickly  to  the  off  position. 

Drum  Controller. — Another  type  of  controller  in  common  use 
is  the  drum  controller.  These  are  used  with  machine  tools  for 
varying  the  speed  and  reversing  the  direction  of  rotation  of  ad- 
justable speed  D.C.  motors  by  means  of  armature  and  field 
resistance.  On  the  larger  sizes  magnetic  blowouts  are  used.  The 
drum  controller  usually  has  two  rows  of  contact  fingers  attached 
to  the  frame  work  of  the  controller  but  insulated  from  it  so  as 

17 


258        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

to  be  electrically  separated  from  each  other.  Between  these 
rows  of  fingers  is  mounted  an  insulated  cylinder  or  drum  which 
is  revolved  by  the  handle.  On  this  drum  are  mounted  copper 
segments  of  different  lengths  which  engage  the  contact  fingers. 
The  length  and  location  of  these  segments  are  such  as  to  make 
different  connections  for  each  position  of  the  controller  handle. 

Drum  controllers  are  also  used  as  master  controllers  with 
contactors  of  various  kinds  to  secure  starting  and  speed  regula- 
tion of  large  A.C.  and  D.C.  motors  as  well  as  the  multiple  unit 
control  of  motor  cars  or  locomotives  on  railway  service.  The 
faceplate  type  of  starter  with  field  regulation  for  D.C.  motors 
may  also  be  considered  as  a  controller 

Starting  Resistance. — In  starting  direct-current  motors  it  is 
usually  necessary  to  insert  a  resistance  in  the  armature  circuit 
to  limit  the  amount  of  starting  current.  As  the  motor  speeds 
up  and  its  counter  E.M.F.  increases  ,this  starting  resistance  is 
gradually  cut  out  until,  when  the  motor  has  reached  full  speed, 
the  resistance  is  all  cut  out  and  the  motor  armature  is  connected 
to  the  full  voltage  of  the  source  of  supply.  These  starting  rheo- 
stats usually  have  various  features;  such  as  no  voltage  and  over- 
load release,  sometimes  combined  with  field  control  and  making 
the  starters  described  in  the  next  few  paragraphs. 

D.C.  Starters. — The  starters  for  use  with  constant  speed  D.C. 
motors  consist  usually  of  a  resistance  to  be  inserted  in  the  arma- 
ture circuit  to  limit  the  amount  of  current  taken  when  starting, 
this  resistance  being  gradually  cut  out  by  the  movement  of  a 
contact  arm  over  a  faceplate  as  the  motor  comes  up  to  speed. 
Such  rheostats  connect  the  motor  field  in  circuit  at  the  first 
step  and  are  provided  with  various  safeguards  such  as  low  voltage 
release,  etc. 

Low  Voltage  Release. — As  a  rule  the  low  voltage  release  con- 
sists of  a  coiled  spring  around  the  pivot  of  the  rheostat  arm  for 
returning  it  to  the  off  position,  and  an  electromagnet  for  retain- 
ing the  arm  in  the  on  position  as  long  as  the  line  voltage  continues 
above  a  predetermined  minimum  value.  On  failure  of  the  line 
voltage  the  magnet  releases  the  arm  which  is  at  once  returned 
automatically  to  the  off  position  by  the  spring. 

To  guard  against  drawing  an  arc  when  the  contact  arm  leaves 
the  first  contact  in  going  to  the  off  position,  this  contact  is  usually 
protected  by  an  arcing  tip  which  provides  a  spring  operated 


INDUSTRIAL  CONTROL  APPARATUS 


259 


break,  or  a  magnetic  blowout  is  furnished  that  extinguishes 
the  arc  that  tends  to  form. 

Typical  D.C.  Starter. — Fig.  164  shows  the  connections  of  a 
typical  D.C.  starter  with  low  voltage  release.  If  the  rheostat 
arm  is  moved  from  the  off  position  shown  in  the  cut  to  the  contact 
R-I,  current  will  flow  from  L  plus  to  the  arm;  from  this  to  contact 
R-I  through  the  regulating  resistance  to  R-II;  thence  through 
the  armature  and  series  field  of  the  motor  to  L.  The  shunt  field 
is  connected  from  R-I  to  L.  Be.utor 

As  the  rheostat  arm  is  being 
moved  from  R-I  to  R-II  there 
is  a  small  drop  in  voltage 
across  the  shunt  field  circuit 
due  to  the  field  current  flow- 
ing through  the  starting  re- 
sistor, but  this  is  so  small  that 
it  may  be  neglected  and  the 
field  can  be  considered  as 
having  full  voltage  impressed 
upon  it.  The  rheostat  arm  is 
provided  with  a  spring  which 
returns  it  to  the  off  position 
and  the  handle  is  released  L  + 
during  the  starting  of  the 
motor.  After  the  motor  has 
been  brought  up  to  speed  and  L  ~ 
the  rheostat  arm  rests  upon 

Contact   R-II  the  low  voltage     Fl°-   164.— D.C.  starter  with  low  voltage 

release. 

release  magnet  holds  the  arm 

in  this  position.  Brush  'B'  bridges  between  the  terminals  'M' 
and  '  N '  so  that  in  the  running  position  the  current  passes  from 
L  plus  to  terminal  *M/  through  the  brush  'B'  to  the  terminal 
'N/  thence  to  the  armature  of  the  motor  through  the  series 
field  to  L-I. 

Multiple  Switch  Starter.— With  the  larger  D.C.  motors  where 
the  starting  conditions  are  severe  the  face  type  of  starter  is  not 
found  satisfactory,  so  recourse  is  had  to  multiple  switch  starters, 
drum  controllers,  or  contactors.  Multiple  switch  starters 
consist  essentially  of  a  number  of  switches  mounted  on  a  panel 
and  a  separate  resistance  usually  of  cast-iron  grids.  The  switches 


260         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

are  mechanically  interlocked  so  that  it  is  necessary  to  close  them 
in  sequence. 

Electrically  Operated  Starter. — In  addition  to  the  hand 
operated  starters,  motor  starters  or  controllers  with  electrically 
operated  switches  or  contactors  are  available  for  almost  every 
conceivable  service.  They  can  be  arranged  to  start,  stop  or 
reverse  the  motor  manually  at  the  will  of  the  operator  or  auto- 
matically at  fixed  limits  and  can  be  set  to  regulate  and  adjust 
the  speed.  Arrangements  can  be  made  to  have  the  motor  auto- 
matically perform  a  predetermined  series  of  operations  and  the 
control  can  be  exercised  from  a  point  near  the  motor  or  from  a 
more  distant  point  more  convenient  for  the  operator. 

Starting  Time. — In  starting  a  motor  a  considerable  amount  of 
energy  is  required  to  overcome  the  inertia  of  the  motor  and  the 
apparatus  it  is  driving  and  a  considerable  amount  of  time  is 
required  to  bring  the  motor  from  a  state  of  rest  up  to  full  speed. 
To  avoid  wrecking  the  motor  this  energy  must  be  admitted 
gradually  and  resistance  in  the  armature  circuit  is  used  for  this 
purpose.  This  resistance  designed  solely  for  starting  purposes  is 
proportioned  to  carry  the  motor  current  only  during  the  short 
time  necessary  to  bring  the  motor  up  to  full  speed.  If  the  time 
taken  in  starting  is  too  long  the  resistance  may  be  injured  by 
overheating  while  if  too  short  the  motor  may  be  damaged  or  the 
supply  circuits  seriously  disturbed. 

Push  Button 
Start        St»p 


FIG.   165. — Automatic    acceleration    with    series    relay. 

Automatic  Starting. — For  these  reasons  a  motor  starter  that  will 
automatically  take  care  of  the  proper  rate  of  acceleration  presents 
many  advantages  and  such  a  starter  can  be  devised  by  means  of 
contactor  switches  and  suitable  relays  which  are  operated  either 
by  the  variation  of  the  voltage  drop  across  a  resistance  as  the 


INDUSTRIAL  CONTROL  APPARATUS 


261 


motor  speeds  up,  or  by  the  decrease  in  current  which  permits  a 
coil  to  drop  its  core  as  shown  in  Fig.  165,  where  acceleration  is 
controlled  by  a  series  relay.  This  is  satisfactory  where  the  volt- 
age does  not  vary  more  than  12^  per  cent,  either  way  from  a 
constant  value.  Fig.  165  shows  the  connections  of  a  shunt  motor 
controlled  by  means  of  two  contactor  switches,  a  push-button 
switch,  and  a  series  relay.  When  the  push  button  is  closed  in  the 
starting  position,  the  coil  of  contactor  No.  1  is  energized,  closing 
the  contactor  and  completing  the  circuit  through  the  series 
relay,  the  starting  resistor,  and  the  armature  of  the  motor. 
When  the  starting  current  has  dropped  to  a  certain  value  the 
current  in  the  series  relay  is  no  longer  sufficient  to  hold  open  the 
contacts  so  that  connection  is  automatically  made  to  the  operat- 
ing coil  of  contactor  No.  2  closing  that  contactor  and  short-cir- 
cuiting the  starting  resistors.  With  very  large  motors  several 
contactors  with  series  relays  are  provided. 


FIG.  166. — Automatic  acceleration  from  counter  E.M.F. 

Counter  E.M.F. — When  a  motor  is  started  from  rest  and 
accelerated  to  full  speed,  the  voltage  across  the  motor  terminals 
increases  as  the  speed  of  the  motor  increases.  If  the  coil  of  a 
magnetic  contactor  is  connected  across  the  motor  brushes  the 
current  in  this  coil  will  increase  as  the  speed  of  the  motor  in- 
creases. Fig.  166  shows  a  starting  arrangement  based  on  the 
counter  E.M.F.  method  and  it  may  be  noted  that  the  operating 
coils  of  the  three  contactors  have  one  side  connected  to  the  motor 
brush  farthest  away  from  the  starting  resistor.  The  other  sides 
of  the  operating  coils  are  connected  to  the  taps  on  the  starting 
resistor,  the  coil  on  switch  No.  1  being  connected  to  R-2  on  the 
resistor.  The  voltage  on  this  coil  is  equal  to  the  line  voltage 
less  the  drop  in  voltage  through  the  first  section  of  the  resistance. 
As  the  speed  of  the  motor  increases  the  counter  E.M.F.  causes 
decrease  in  the  armature  current.  This  reduces  the  drop  to  the 
first  section  of  the  starting  resistance.  The  voltage  on  the 


262        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


Magnet  Tcke 
Magnet  Core  C] 

Operating  OoU      / 

Closing  Contact! 


operating  coil  of  switch  No.  1  is  gradually  increased  until  this 
switch  closes.  Switch  No.  2  has  its  operating  coil  connected  to 
R-3  on  the  starting  resistor.  The  voltage  on  this  coil  is  increased 
by  the  closure  of  switch  No.  1.  The  increase  in  current  causes  a 
considerable  drop  in  the  second  section  of  the  starting  resistance. 
As  this  current  gradually  decreases  due  to  the  increased  speed  of 
the  motor,  switch  No.  2  closes.  Switch  No.  3  is  connected 
across  the  motor  armature  and  closes  when  the  counter  E.M.F.  of 
the  motor  is  nearly  equal  to  the  line  voltage.  The  main  contact- 
ors for  closing  the  main  +  and  —  circuits  are  not  shown  in  the 
diagram. 

Series  Lockout. — Another  scheme  of  acceleration  frequently 
used  is  the  series  lockout  method.  With  this  arrangement  the 
magnetic  contactor  is  provided 
with  a  series  coil  and  does  not 
require  a  separate  relay  for  con- 
trolling it.  The  closing  of  the 
magnetic  contactor  depends  upon 
the  saturation  of  the  iron  in  one 
portion  of  the  magnetic  circuit. 
This  can  be  understood  from  the 
diagram  of  a  contactor  of  this 
design  shown  in  Fig.  167.  The 
flux  or  magnetism  in  the  iron  is 
caused  by  the  current  flowing 
through  the  operating  coil.  This 
flux  passes  through  the  air  gaps  in 

the  armature  of  the  contactors.  Part  of  this  flux  passes  from 
the  armature  through  the  armature  brackets  to  the  magnetic 
yoke  and  thence  to  the  magnet  core.  Another  part  of  the 
flux  passes  from  the  armature  through  the  tailpiece  of  the 
magnet  yoke.  The  flux  through  this  last  circuit  exerts  a  pull 
which  prevents  the  contactor  from  closing.  The  magnetic  path 
through  the  armature  brackets  is  of  small  cross-section  so  that 
when  the  current  flowing  through  the  operating  coil  exceeds  a 
certain  value  it  becomes  saturated  and  forces  the  balance  of  the 
flux  through  the  tailpiece  holding  the  contactor  open.  As  the 
current  decreases,  the  flux  in  the  saturated  armature  bracket 
remains  constant  and  the  flux  through  the  tailpiece  decreases 
until  it  is  not  sufficient  to  hold  the  contactor  open.  The  switch 
can  be  adjusted  to  close  at  a  predetermined  value  by  changing  the 


FIG.    167. — Lockout   contactor. 


INDUSTRIAL  CONTROL  APPARATUS  263 

hold  out  air  gaps  between  the  tailpiece  and  the  magnet  yoke 
by  means  of  a  calibrating  screw. 

Lockout  Contactor. — The  success  of  starters  with  acceleration 
control  such  as  previously  described,  depends  largely  on  the 
contactors  or  contactor  switches.  Contactors  are  switches  or 
circuit  breakers  which  are  held  in  the  closed  position  by  some 
auxiliary  power  such  as  a  solenoid  or  compressed  air.  A  typical 
contactor  is  very  similar  to  the  lockout  contactor  shown  in 
Fig.  167,  using  a  shunt  coil  instead  of  the  series  coil  and  omitting 
the  tail  piece,  the  damping  coil  and  similar  features,  so  that  as 
soon  as  the  shunt  coil  is  energized  the  contactor  is  closed 
against  the  pressure  of  a  spring.  Contactors  are  built  both  for 
D.C.  and  A.C.  operation  and  are  made  single  pole  and  multi- 
pole,  single  throw  and  double  throw,  in  various  capacities. 
The  main  arcing  contacts  are  usually  protected  by  means  of  a 
magnetic  blowout. 

These  contactors  are  ordinarily  used  in  connection  with  a 
master  switch  or  controller  and  protective  relay  switches  of 
various  kinds  to  insure  the  performance  of  various  functions, 
such  as  the  automatic  cutting  in  and  out  of  resistance  in  the  sec- 
ondary of  an  induction  motor  to  maintain  constant  input  to  a 
flywheel  set  or  any  similar  feature  that  may  be  desired. 

A.C.  Starters. — Starters  for  A.C.  motors  may  be  divided  into 
two  classes;  those  used  with  motors  having  a  squirrel-cage  or 
short-circuited  secondary  and  those  for  motors  having  a  wound 
secondary.  In  the  former  case  the  starting  is  done  by  impressing 
on  the  primary  a  voltage  sufficient  to  induce  in  the  short-cir- 
cuited secondary  the  current  required  to  develop  the  proper 
starting  torque,  and  then  transferring  the  primary  connections  to 
full  voltage. 

Wound  Rotor  Motors. — With  motors  having  a  wound  sec- 
ondary it  is  customary  to  connect  the  primary  to  full  voltage  at 
starting  with  the  secondary  short-circuited  through  a  resistance. 
As  the  motor  speeds  up  this  secondary  resistance  is  cut  out  in  one 
or  more  steps  until  at  full  speed  the  secondary  is  short-circuited. 

Squirrel-cage  Motor. — With  squirrel-cage  motors  up  to  about 
7^-2  H.P.  it  is  usually  feasible  to  connect  the  primary  immediately 
to  the  full  line  voltage  without  drawing  an  abnormal  current 
from  the  line. 

For  textile  work  where  small  motors  are  used  in  large  numbers 
on  circuits  up  to  550  volts,  a  special  oil  immersed  switch  is  used, 


264         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


this  being  made  single  throw  for  ordinary  service,  double  throw 
when  reversing  is  wanted. 

Auto  Transformer  Starting. — Under  normal  conditions  the 
most  satisfactory  means  of  obtaining  the  reduced  voltage  for 
starting  induction  motors  with  squirrel-cage  secondaries  is  by  the 
use  of  auto  transformers,  the  connections  for  this  method  of 
starting  being  shown  diagrammatically  in  Fig.  168,  the  switching 


Starting  Connections 


Running  Connections 


FIG.  168.  —  Auto-starter  connections. 

mechanism  being  omitted  for  the  sake  of  simplicity.  In  the 
starting  position  the  voltage  at  the  motor  primary  which  is  con- 
nected to  the  auto  transformer  is  cut  down  by  the  auto  trans- 
formers from  200  to  130  in  this  particular  case.  The  current  in 
the  motor  primary  is  200  amperes  but  the  line  current  due  to 
the  transformer  action  is  only  130  amperes.  In  the  running 
position  the  motor  primaries  are  connected  directly  across  the 
line  and  the  auto  transformers  are  disconnected  at  one  end  so 
that  their  losses  are  eliminated. 

Starting  Voltage.  —  The  starting  voltage  of  induction  motors 
should  not  be  greater  than  is  required  for  the  starting  torque; 
hence  the  starting  voltage  should  be  adjusted  to  the  service 
conditions.  The  auto  transformers  supplied  for  starting  induc- 
tion motors  are  provided  with  taps  permitting  the  choice  of  any 
one  of  several  voltages.  The  auto  transformers  are  designed 
for  starting  service  only  and  are  not  intended  to  be  left  perma- 
nently in  circuit. 

Auto  Starters.  —  The  auto-starter  switches  or  circuit  breakers 
are  made  of  various  types,  usually  either  with  wedge  contacts 
or  brush  contacts  depending  on  the  current  to  be  handled.  The 
equivalent  of  the  double-throw  switch  is  usually  furnished, 
one  throw  energizing  auto  transformers  and  connecting  the 
motor  to  low  voltage  taps  for  starting  and  the  second  throw  con- 


INDUSTRIAL  CONTROL  APPARATUS  265 

necting  the  motor  directly  to  full  voltage  for  running.  The 
second  throw  usually,  though  not  always,  completely  disconnects 
the  auto  transformers  from  the  circuit. 

Automatic  Protection. — With  auto  starters  this  is  usually 
secured  by  means  of  overload  trip  coils,  either  connected  directly 
in  the  circuit  or  operated  from  current  transformers.  Usually 
the  overload  protection  is  only  in  the  running  position.  With 
certain  types  of  auto-starter  switches  the  overload  release  device 
consists  of  two  solenoids  with  plungers  in  two  different  phases 
and  an  oil  filled  dashpot  on  each  solenoid  plunger  gives  an  inverse 
time  element  feature.  The  switch  contacts  usually  trip  inde- 
pendently of  the  handle  so  that  the  switch  cannot  be  held  closed 
on  an  overload. 

Automatic  Starting. — By  certain  modifications  these  auto 
starters  can  be  made  suitable  for  automatically  starting  and 
stopping  induction  motors  that  are  used  for  driving  pumps  or 
compressors  so  that  the  level  of  liquids  in  reservoirs  or  the  pres- 
sures in  a  compressed  air  system  can  be  maintained  within 
predetermined  limits  without  supervision.  The  float  type  auto 
starter  is  applicable  to  motor  driven  pumps  that  supply  cisterns 
and  reservoirs,  sumps,  sewers,  etc.,  if  the  pump  is  near  enough  so 
that  the  rising  and  falling  of  a  float  in  the  reservoir  or  sump  may 
be  communicated  by  rope  drive  to  a  weight  device  that  operates 
the  auto  starter. 

With  the  pressure  type  regulator  a  pressure  gauge  switch  and 
relay  are  supplied  that  work  in  connection  with  an  electromag- 
netically  operated  valve,  two  cylinders  and  a  spring  and  ratchet 
device  to  move  the  auto-starter  switch  through  the  starting 
position  to  the  running  position  or  return  it  to  the  off  position. 

Synchronous  Motor. — Where  self-starting  synchronous  motors 
are  used,  they  are  provided  with  a  squirrel-cage  winding  on  the 
rotor  in  addition  to  the  usual  field  poles  and  field  coils  and,  owing 
to  this  squirrel-cage  winding,  they  are  started  up  as  induction 
motors  and  controlled  by  the  same  type  of  starting  devices.  Other 
apparatus  such  as  field  rheostats  and  field  switches  are  necessary 
to  take  care  of  the  motor  when  in  the  normal  running  condition. 

Phase  Wound  Motor. — With  induction  motors  having  phase- 
wound  secondaries  the  method  of  control,  as  mentioned  previ- 
ously, is  to  connect  the  primary  circuit  directly  to  the  high 
voltage  line  with  the  secondary  winding  short-circuited  through  a 
resistance  which  is  cut  out  in  one  or  more  steps  as  the  motor 


266        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

comes  up  to  speed.  The  switch  or  circuit  breaker  in  the  primary 
circuit  is  made  suitable  for  the  voltage  and  capacity  of  the  motor 
while  the  secondary  is  taken  care  of  by  various  devices  such  as 
drum  controllers,  butt  contact  switches,  contactors,  etc. 

Mill  Work. — For  reversing  mill  or  hoisting  work  using  induc- 
tion motors  with  wound  secondaries,  many  very  ingenious  and 
highly  satisfactory  installations  have  been  put  in  service  using 
solenoid  operated  magnet  switches  or  contactors  for  the  secon- 
dary and  occasionally  for  the  primary  circuits.  These  are  worked 
from  a  master  controller  or  similar  device  or  are  operated  auto- 
matically by  the  positions  of  the  rolls,  hoist,  etc.  Automatic 
acceleration  can  be  obtained  in  the  same  manner  as  indicated  on 
Figs.  165  and  166,  and  various  safeguards  such  as  dynamic  brak- 
ing can  be  employed. 

Flywheel  Sets. — Another  application  for  contactor  control 
with  automatic  features  is  with  flywheel  motor-generator  sets 
using  a  very  heavy  flywheel  in  connection  with  a  D.C.  generator 
and  an  A.C.  motor  with  wound  secondary.  The  power  put 
into  the  flywheel  or  delivered  up  by  it  depends  on  the  variation  in 
speed  of  the  motor  generator  and  by  varying  the  resistance  in  the 
motor  secondary  this  speed  regulation  can  be  secured.  By  the 
use  of  relays  similar  to  those  described,  the  input  to  the  motor  and 
consequently  the  load  on  the  A.C.  system  can  be  kept  practically 
constant  while  the  output  of  the  D.C.  generator  supplying  power 
to  a  D.C.  hoist  or  rolling  mill  motor  is  undergoing  wide  fluctua- 
tions, the  energy  in  the  flywheel  taking  care  of  the  difference 
between  the  constant  input  and  the  variable  output. 

Automatic  Substations. — An  application  of  contactor  control 
of  rapidly  increasing  importance  is  the  automatic  substation  by 
means  of  which  rotary  converters,  motor  generators,  or  other 
transforming  devices  are  cut  into  and  out  of  service  automatically 
with  the  varying  demands  on  the  system.  Descriptions  of 
these  automatic  substations  are  given  later. 


CHAPTER  XI 
SWITCHBOARDS— GENERAL  INFORMATION 

In  taking  up  the  question  of  switchboards,  after  having  de- 
voted many  pages  of  this  book  to  a  consideration  of  the  apparatus 
for  power  plant  control,  it  should  be  noted  that  the  term  switch- 
board as  here  used  is  applied  to  the  collection  of  panels,  pedestals, 
posts,  control  desks,  etc.,  on  which  are  mounted  the  instruments, 
relays,  switches,  circuit  breakers,  etc.  so  that  from  this  point  of 
view  the  switchboard  is  practically  a  collection  of  switching 
apparatus  assembled  in  a  logical  manner  to  facilitate  the  control 
of  various  electrical  circuits. 

Diagram. — The  apparatus  previously  described  can  be  com- 
bined in  various  ways  to  secure  the  results  desired  in  power 
plant  control.  These  various  combinations  are  usually  expressed 
in  the  form  of  a  diagram  of  connections  before  any  attempt  is 
made  to  decide  on  the  switching  equipment. 

D.C.  Connections. — For  direct-current  service  the  main  con- 
nections usually  embody  a  knife  switch  and  fuses  or  carbon  cir- 
cuit breakers  for  securing  the  automatic  protection.  In  most 
cases,  only  a  single  set  of  bus  bars  is  employed,  and  the  connec- 
tions are  very  simple. 

A.C.  Connections. — For  alternating-current  service  the  con- 
nections are  usually  more  complicated,  and  as  the  plants  are 
larger  and  more  important,  greater  flexibility  is  usually  provided. 

In  making  up  a  preliminary  diagram  it  is  usual  to  show  all  of 
the  circuits  whether  direct  current,  single  phase,  or  polyphase 
by  means  of  a  single  line  per  circuit  and  to  indicate  oil  circuit 
breakers,  disconnecting  switches  and  similar  devices  by  simple 
conventional  signs. 

Single  Line  Diagram. — In  these  single  line  diagrams  it  is 
seldom  necessary  to  show  the  metering  and  relaying  equipment, 
and  usually  the  diagram  is  reduced  to  its  simplest  elements, 
merely  locating  the  main  generators,  transformers,  feeders,  oil 
circuit  breakers,  disconnecting  switches,  and  bus  bars. 

267 


268        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Typical  Connections. — Fig.  169  shows  a  number  of  typical 
connections  between  generator  and  bus  circuits.  On  this  dia- 
gram the  generators  are  represented  by  large  circles,  the  oil 
circuit  breakers  by  rectangles,  the  disconnecting  switches  by 
two  small  circles,  transformers  by  two  saw  tooth  lines,  and  out- 
going feeders  by  an  arrow  head.  While  the  main  connections 
are  fairly  evident  from  the  diagram,  the  following  notes  point 
out  some  of  the  principal  features. 

Fig.  'A'  shows  a  single-bus  system  with  a  generator  feed- 
ing through  an  oil  breaker  and  a  disconnecting  switch  to  a  bus; 
this  being  about  the  simplest  possible  arrangement  although  oc- 
casionally the  disconnects  are  omitted. 

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FIG.    169. — Typical   connections   of  generators   and   bus. 

'B'  shows  a  double-bus  system  with  a  main  breaker,  two 
selector  breakers  and  disconnects  for  isolating  the  selector 
breakers  from  the  two  sets  of  busses.  With  this  arrangement 
there  are  two  breakers  in  series  between  any  generator  or  bus 
or  any  feeder  or  bus,  this  permitting  the  testing  out  of  each 
breaker  independently  before  tying  in  the  circuit.  This  scheme 
was  a  favorite  one  in  the  early  days  of  oil  circuit-breaker  develop- 
ment when  complete  reliance  was  not  placed  on  the  satisfactory 
performance  of  oil  breakers.  The  disconnects  permit  isolating 
either  selector  breaker  from  the  bus,  but  owing  to  the  absence 
of  any  disconnecting  switches  between  the  main  breaker  and  the 
selectors,  it  is  necessary  to  shut  down  a  circuit  before  any  work 
can  be  done  on  any  of  the  oil  breakers. 

'E'  shows  a  similar  arrangement  with  the  addition  of  dis- 
connects on  each  side  of  the  selector  breakers  as  well  as  discon- 


SWITCHBOARDS— GENERAL  INFORMATION  269 

nects  between  the  generator  breaker  and  the  common  connection 
to  the  two  selectors.  With  this  arrangement  either  of  the  selector 
breakers  can  be  completely  isolated  by  means  of  their  disconnects 
without  shutting  down  the  generator  or  feeder  or  shutting  down 
the  bus.  The  disconnects  between  the  common  connection  and 
the  generator  breaker  are  utilized  for  isolating  the  generator 
breaker  in  case  the  selectors  are  to  be  used  for  tying  together  the 
two  sets  of  busses. 

'  D '  shows  a  somewhat  simpler  arrangement  with  two  sets 
of  busses  and  two  selector  breakers  omitting  any  main  generator 
breaker.  This  is  a  very  common  arrangement  where  two  sets  of 
busses  are  desired. 

'  C '  shows  a  generator  with  a  generator  breaker  and  a  certain 
number  of  disconnects  so  arranged  that  the  generator  can  be 
connected  either  to  the  bus  or  to  the  low  tension  side  of  a  trans- 
former bank  or  the  low  tension  side  of  a  transformer  bank  can 
be  connected  to  the  bus,  while  the  generator  is  shut  down. 

'F'  shows  a  modification  of  this  arrangement  with  the  genera- 
tor tied  in  solidly  on  the  low  tension  side  of  its  step  up  transformer 
with  a  breaker  and  disconnects  on  the  high  side  of  the  trans- 
former, breaker  and  disconnects  for  connecting  the  machine 
to  the  station  auxiliary  bus. 

*G'  shows  an  arrangement  very  similar  to  'C,'  but  with  an 
additional  oil  breaker  to  facilitate  connecting  the  generator  to 
the  main  bus. 

'  H '  shows  an  arrangement  of  a  generator  with  one  oil  breaker 
and  two  sets  of  disconnects  for  connecting  the  machine  to  either 
of  two  sets  of  busses. 

'I'  shows  two  generators  feeding  through  breakers  and  dis- 
connects to  a  generator  bus.  This  generator  bus  in  turn  connects 
through  breaker  and  disconnects  to  the  main  bus,  or  through 
another  breaker  and  disconnects  to  the  low  tension  side  of  a  trans- 
former bank.  With  this  arrangement  the  two  generators  are 
considered  essentially  as  a  single  unit  and  are  arranged  for  feed- 
ing their  own  transformer  bank,  or  tieing  to  a  main  bus  bar. 

'J'  is  essentially  the  same  arrangement  as  'D'  except  that 
one  bus  is  considered  as  the  main  bus,  and  the  other  as  a  trans- 
fer bus  for  emergency  purposes. 

'K'  shows  a  combination  of  one  generator  and  one  trans- 
former bank  with  a  total  of  three  breakers  and  suitable  discon- 
nects so  that  the  generator  may  be  connected  directly  to  its  own 


270        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

transformer  bank  or  the  generator  or  transformer  connected  to 
the  transfer  bus.  A  slight  modification  of  this  scheme,  using 
the  same  number  of  breakers,  has  one  breaker  connecting  the 
generator  directly  to  the  transformer;  a  second  breaker  connect- 
ing the  generator  to  the  bus,  and  the  third  breaker  connecting  the 
transformer  to  the  bus,  so  there  are  always  two  paths  between 
the  generator  and  transformers. 

'L'  shows  an  arrangement  of  main  bus,  selector  bus,  feeder 
group  busses,  etc. 

The  remaining  schemes  'M'  to  'U'  inclusive,  are  slightly 
more  complicated,  but  are  all  based  on  the  main  connections 
used  in  actual  plants.  As  practically  all  of  the  connections  indi- 
cated in  Fig.  169,  can  be  utilized  either  for  generator  or  for  feeder 
circuits,  they  may  be  considered  as  forming  the  elements  of  dia- 
gram construction,  and  most  of  the  more  complicated  diagrams 
are  combinations  of  the  various  methods  indicated. 

Instrument  Transformers. — After  completing  the  elementary 
single  line  diagram,  it  is  frequently  a  good  plan  to  locate  the 
current  and  the  potential  transformers  needed  for  the  operation 
of  instruments  and  relays,  and  then  to  prepare  a  detail  diagram 
showing  the  interconnections  of  these  various  features. 

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1    )  f    2 

FIG.  170. — Diagram   of   single   bus   system. 

Single  Bus. — For  simple  plants  where  economy  is  of  prime 
importance,  the  straight  single-bus  system  as  indicated  in  Fig. 
170,  is  usually  adopted.  This  diagram  shows  3  generators  and 
six  outgoing  feeders,  each  circuit  being  provided  with  an  oil 
circuit  breaker  and  a  disconnecting  switch,  and  the  current 
transformers  being  located  in  such  a  position  as  to  carry  the  com- 
bined output  of  all  the  generators.  With  a  single-bus  system 
such  as  shown,  bus  bar  trouble,  which  is  very  infrequent,  necessi- 
tates complete  shut-down.  To  replace  the  oil,  inspect  or  adjust 
any  circuit  breaker,  it  is  necessary  to  shut  down  the  particular 
circuit  involved,  but  it  is  not  necessary  to  shut  down  the  entire 
plant,  as  disconnecting  switches  are  provided  for  isolating  the 
breaker  from  the  bus.  A  still  cheaper  and  simpler  arrangement 


SWITCHBOARDS— GENERAL  INFORMATION  271 

adopted  for  small  boards,  dispenses  with  the  disconnects,  but 
this  makes  it  necessary  not  only  to  shut  down  a  particular  cir- 
cuit, but  also  the  entire  plant,  unless  the  voltage  is  so  low  that  the 
repair  man  is  willing  to  risk  working  on  the  breaker  while  the  bus 
is  alive. 

Double  Bus. — By  adopting  a  double-bus  system  of  one  breaker 
and  two  disconnects  per  circuit,  one  bus  can  be  shut  down  for 
inspection  of  the  board  or  insulators  without  shutting  down  any 
circuit  by  opening  all  of  the  disconnects  tied  on  to  that  bus.  If 
any  particular  feeder  is  giving  trouble  due  to  grounds  or  frequent 
short  circuit,  it  may  be  connected  to  one  bus  with  one  generator, 
and  the  rest  of  the  plant  connected  to  the  other  bus.  By  using 

i— ri    i  J    j  1    i  FFF 
£  $$  $$  $$ 

g    g   V    V 


Ti. 
Brukcn. 


FIG.   171. — Diagram   of   double   bus   system. 

the  double-bus  system,  with  two  breakers  per  circuit,  any  breaker 
can  be  cut  out  of  service  for  inspection  or  repair  without  shutting 
down  a  circuit  or  without  shutting  down  either  bus  provided 
suitable  disconnects  are  employed.  A  bus  can  also  be  shut  down 
at  any  time  to  have  insulators  cleaned  or  connections  altered. 
A  typical  arrangement  employing  the  double-bus,  double  cir- 
cuit-breaker system  is  shown  in  Fig.  171,  this  showing  two  gene- 
rators, three  outgoing  feeders  and  a  bus  tie  breaker.  In  many 
systems  employing  the  double-bus  and  double  circuit-breaker 
equipment,  the  breakers  are  interlocked  so  that  normally  a  cir- 
cuit can  only  be  connected  to  one  bus  at  a  time.  The  tie  breaker 
is  used  for  connecting  the  two  busses  together,  and  provision  is 
made  for  synchronizing  around  the  tie  breaker.  In  any  case, 
however,  where  it  is  desirable  to  be  able  to  transfer  a  generator 
or  feeder  from  one  bus  to  the  other  without  opening  the  circuit, 
the  breakers  are  not  interlocked.  In  this  case,  the  tie  breaker 
is  dispensed  with  and  when  it  is  desired  to  tie  the  two  busses 
together,  two  of  the  generator  breakers  or  feeder  breakers  are 
connected  in  at  the  same  time. 

Ring  Bus. — Where  stations  of  moderate  size  require  great 
flexibility  and  maximum  security  and  where  due  to  the  low  vol- 


272        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

tage  employed,  the  current  in  the  bus  is  apt  to  be  excessive  unless 
limited  to  the  full  output  of  one  machine,  the  arrangement  shown 
in  Fig.  172  is  adopted.  With  this  arrangement,  each  generator 
and  feeder  is  provided  with  a  breaker  and  the  equivalent  of  double 
throw  disconnects.  The  busses  are  practically  divided  into  four 
sections  which  sections  can  be  tied  together  to  form  a  complete 
ring  bus. 


Fwdcr,  ^^  V_X  Fwdcr 

FIG.   172. — Diagram  of  ring  bus  system. 


O  Q  LJ     LJ  LJ  O 

©      ©    Li.  ©      © 

FIG.   173. — Diagram  of  typical  plant  with  sectioned  bus. 

Sectioned  Bus. — Fig.  173  shows  a  plant  controlling  four 
generators,  four  step-up  transformer  banks  and  two  outgoing 
lines  using  the  single  sectionalized  bus  system.  Each  circuit  is 
provided  with  one  breaker  and  one  set  of  disconnects,  but  the 
busses  are  so  sectionalized,  that  normally  each  generator  will 
tie  in  with  its  own  transformer  bank,  and  two  transformer  banks 
will  normally  supply  current  to  their  own  outgoing  line  circuits. 
The  low  tension  bus  is  so  sectionalized  by  means  of  disconnecting 
switches  that  the  local  feeders  may  be  fed  from  either  half  of  the 


SWITCHBOARDS— GENERAL  INFORMATION 


273 


station.  A  modification  of  this  system  utilizing  the  same  number 
of  low  tension  disconnects,  utilizes  the  four  sets  of  disconnects, 
shown  for  sectionalizing  the  low  tension  bus,  for  tying  the  com- 
bined generator  and  transformer  bus  to  a  low  tension  transfer 
bus,  which  low  tension  transfer  bus  supplies  the  current  to  the 
local  feeders. 

Special  Bus. — Fig.  174  shows  the  general  scheme  of  connections 
adopted  for  the  original  plant  of  the  Rio  Janeiro  Tramways  Light 
&  Power  Company  controlling  six  generators,  six  banks  of  step-up 

Outgoin,  Lino 


r-o-r 


i  jj  yj  iji.ii  yi  in 

o_.    o-l    0-,    oJ    c-,     M  I"BK"««  M    »_    <_!    <>_   o_l    <_ 


O  CD  0 


tfftfttyjj 

©° 


P  u 


FIG.  174. — Diagram  of  connections  for  Rio  de  Janeiro. 

transformers  and  four  outgoing  transmission  lines.  The  plant  is 
normally  operated  with  each  generator  connected  to  the  low 
tension  side  of  its  own  transformer  bank.  Suitable  breakers  and 
disconnects  are  provided  however,  so  that  any  generator  may  be 
connected  to  the  low  tension  bus  by  a  second  oil  breaker  or  the 
transformer  bank  may  be  connected  to  the  low  tension  bus  by  dis- 
connecting switches.  The  low  tension  bus  is  sectioned  in  the 
middle  by  means  of  breaker  with  disconnects,  and  the  low  ten- 
sion feeder  bus  can  be  supplied  from  either  half  of  the  main  low 
tension  bus  through  proper  disconnects.  This  feeder  bus  with 


274        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

auto  transformers  is  arranged  for  furnishing  current  to  the  ex- 
citer motors. 

On  the  high  tension  side  each  transformer  bank  is  provided 
with  a  breaker  and  double-throw  disconnects  connecting  to 
either  of  two  high  tension  busses;  these  high  tension  busses  are 
each  split  in  the  middle  by  means  of  section  breakers  and  are 
tied  together  through  tie  breakers.  The  four  outgoing  lines 
are  each  provided  with  two  sets  of  disconnects  for  connecting  to 
either  of  the  two  sets  of  busses  and  an  oil  breaker.  As  the 
double-throw  disconnects  on  the  high  tension  side  are  of  the 
selector  type,  any  circuit  can  be  connected  to  two  busses  at 
the  same  time,  so  that  when  it  is  desired  to  transfer  a  transformer 
or  line  circuit  from  one  bus  to  the  other  this  can  readily  be  done 
and  the  work  is  facilitated  by  the  use  of  the  tie  breakers  so  that 
no  current  will  ever  have  to  be  opened  on  the  disconnecting 
switches. 

Flexibility. — Different  engineers  have  their  own  ideas  as  to  the 
amount  of  flexibility  necessary  or  advisable  in  any  particular 
plant,  and  the  system  adopted  is  frequently  a  compromise  so  as 
to  secure  a  reasonable  amount  of  flexibility  with  the  minimum 
amount  of  switching  equipment. 

For  the  simpler  plants  using  direct-control,  panel  mounted, 
devices,  usually  the  single-throw  system  is  adopted.  For  some- 
what larger  plants  utilizing  distant  mechanical  control  oil  circuit 
breakers,  the  single-bus  or  double-bus  system  can  be  used  and 
normally  sufficient  space  can  be  made  available  for  the  location 
of  one  or  more  sets  of  bus  bars  and  suitable  disconnecting 
switches. 

For  the  largest  plants  using  electrically  operated  breakers, 
practically  unlimited  choice  is  available  as  to  the  schemes  of 
connections  to  be  employed. 

In  the  descriptions  that  follow  of  switchboard  panels,  some  of 
these  features  of  main  connections  are  considered  more  fully, 
while  the  more  complicated  systems  utilizing  distant  control 
devices  are  considered  in  connection  with  structures  and  station 
layout  arrangement. 

Largest  Builders. — The  main  differences  in  the  switchboards 
built  by  different  manufacturers  lie  in  the  apparatus  mounted  on 
the  panels  and  where  the  switchboard  builder  is  also  a  manu- 
facturer of  instruments,  switches,  breakers,  etc.,  he  naturally 
prefers  to  use  his  own  equipment.  The  two  largest  electrical 


SWITCHBOARDS— GENERAL  INFORMATION  275 

manufacturers  in  the  United  States  that  build  generators,  trans- 
formers, synchronous  converters  and  other  power  plant  equip- 
ment are  the  General  Electric  Company  and  the  Westinghouse 
Electric  &  Manufacturing  Company,  and  the  two  of  them  together 
do  the  largest  portion  of  the  switchboard  business  in  the  United 
States,  usually  arranging  to  furnish  the  switching  equipment  for 
the  control  of  their  own  machines,  although  this  is  not  always 
the  case. 

The  general  features  of  switchboard  design  of  the  two  com- 
panies in  question  have  naturally  been  the  result  of  their 
apparatus  development  and  the  competition  for  switchboard 
business  has  led  to  the  desire  for  standardization  to  bring  down 
manufacturing  costs  and  to  expedite  production. 

Other  Builders. — There  are  of  course  a  number  of  other  switch- 
board builders  competing  for  the  switchboard  business,  particu- 
larly for  the  direct-current  light  and  power  work  where  there  are 
many  more  different  builders  of  generators  than  there  are  in  A.C. 
work.  The  D.C.  light  and  power  switchboards  for  large  office 
buildings  are  usually  made  according  to  specifications  of  an 
architect  or  engineer  and  usually  do  not  conform  to  any  particular 
standard  of  construction.  For  this  class  of  switchboard  work, 
the  independent  contractor  and  the  small  builder  is  often  in  a 
better  position  to  carry  out  the  architect's  ideas  than  a  large 
manufacturing  company  whose  shop  routine  is  designed  especi- 
ally for  quantity  production  of  standard  equipment. 

Treatment. — In  treating  the  question  of  switchboards  the 
general  features  will  be  taken  up  first,  then  the  simpler  D.C. 
boards,  then  the  more  complicated  ones,  these  in  turn  being 
followed  by  the  A.C.  boards  that  are  usually  more  involved  and 
frequently  affect  the  station  design  very  materially.  While  the 
illustrations  may  seem  to  show  the  equipment  of  one  builder 
more  often  than  that  of  others,  this  does  not  imply  any  idea  that 
it  represents  the  actual  relative  proportion  in  which  the  various 
types  are  used  in  actual  practice,  but  merely  that  the  author 
found  it  simpler  to  utilize  the  illustrations  that  were  easiest  to 
obtain. 

Differences. — In  the  usual  illustration  of  a  switchboard  it 
takes  an  expert  to  distinguish  what  type  of  carbon  breaker  or 
knife  switch  is  shown.  Where  oil  circuit  breakers  are  used  the 
cover  plates  of  different  designs  are  more  or  less  a  distinguishing 
feature,  and  whether  the  meters  are  shown  as  rectangular  or 


276        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


circular  is  often  a  clue  to  the  builder  of  an  A.C.  switchboard, 
but  comparatively  few  changes  would  be  necessary  to  alter  the  ap- 
pearance of  the  usual  switchboard  so  that  it  would  be  difficult 
to  tell  what  maker  was  responsible  for  it. 

Standards. — As  a  result  of  the  standardizing  process  the  general 
practice  of  many  switchboard  makers  is  becoming  more  and  more 
similar  and  one  of  the  main  ideas  of  the  first  part  of  this  chapter 
will  be  to  point  out  the  gradual  evolution  of  this  standard  practice 
and  to  give  the  reasons  for  various  features.  These  reasons  of 
course  apply  broadly  to  all  switchboards  both  of  the  direct-control 
and  the  distant-control  types.  However,  the  former  applying 
to  moderate  capacity  plants  followed  "standard  practice" 
more  closely  than  the  latter  due  to  the  many  special  features  in 
large  plants. 

The  earliest  so-called  panel  boards  were  made  of  wooden  panels 
with  the  various  switches,  instruments,  etc.,  each  on  its  own 
base  and  attached  to  the  wooden  panel  with  the  wiring  either  on 
the  front  or  the  rear. 


•  e 


mmmm 


FIG.  175. — Wooden  switchboard  for  Korea  built    1887. 

Wooden  Board. — Fig.  175  shows  a  board  of  this  type, 
built  about  1887  for  Korea  and  used  for  the  control  of 
four  direct-current  low  voltage  generators  and  eight  feeder 
circuits.  Each  generator  was  provided  with  a  pilot  lamp,  an 
ammeter,  a  single-pole  carbon  break  circuit  breaker,  a  2-pole 
switch  and  a  rheostat.  Each  of  the  eight  feeder  circuits  had  a 


SWITCHBOARDS— GENERAL  INFORMATION 


277 


2-pole  switch  and  a  voltmeter  was  furnished  with  a  voltmeter 
switch  for  connecting  it  to  various  circuits.  The  switchboard 
was  made  of  tongued  and  grooved  lumber  with  all  of  the  wiring 
on  the  back  and  was  strictly  up  to  date  at  the  time. of  its  manu- 
facture. 

The  next  step  in  advance  was  the  elimination  of  the  wooden 
panel  or  framework.  Each  piece  of  apparatus  was  then  mounted 
on  a  marble  slab  and  was  arranged  for  placing  in  an  angle  iron 
frame  work  and  switchboards  were  made  by  combining  the 
necessary  ammeters,  voltmeters,  switches  and  rheostat  slabs 
to  make  the  panels  for  the  different  generators,  feeders,  etc. 


FIG.   176. — Panel  Switchboard  Brush  Electric  Co.  of  Baltimore  1894. 

Old  Panel  Board. — Fig.  176  shows  a  large  double-deck  board 
of  this  design  supplied  to  the  Brush  Electric  Company  of  Balti- 
more about  1894  and  used  for  the  control  of  A.C.  and  D.C. 
generators  and  feeders.  The  five  panels  to  the  left  on  the 
lower  floor  were  used  for  the  control  of  five  1000  K.V.A.  2-phase 
A.C.  generators  operating  independently,  those  being  practically 
two  single-phase  machines  with  their  armatures  coupled  together 
mechanically  and  displaced  through  an  angle  corresponding  to 
90  electrical  degrees.  Each  panel  had  a  pilot  lamp,  two  am- 
meters, two  voltmeters,  two  2-pole  double-throw  switches,  two 


278      SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


sets  of  field  plugs  and  two  rheostat  faceplates  for  the  two  sepa- 
rate field  circuits  used  with  the  2-phase  machines.  The  next 
two  panels  with  the  bell  and  clock  were  station  panels,  the  next 
four  exciter  panels,  and  the  last  two  D.C.  feeder  panels.  The 
balcony  was  devoted  to  A.C.  feeder  circuits  each  panel  control- 
ling a  single-phase  feeder  which  could  be  transferred  by  means  of 
plugs  and  cables  and  a  2-pole,  double-throw  switch  from  any 
one  of  eight  single-phase  bus  bars  to  any  other  bus. 

This  form  of  construction  was  entirely  fireproof  but  various 
disadvantages  ultimately  led  to  its  being  superseded  by  the 
modern  design  of  panel  switchboards  with  the  apparatus  grouped 
on  panels  made  of  one  or  more  comparatively  large  pieces  of 
marble  or  slate. 

Present  Standards. — These  lines  of  switchboards  manufac- 
tured by  various  companies  are  the  result  of  careful  study  of 

requirements.  In  general,  the 
standard  switchboards  may  be 
divided  into  two  types  with  re- 
gard to  their  framework.  The 
cheaper  and  smaller  panels  are 
mounted  on  a  framework  of  gas 
pipe  and  usually  comprise  panels 
about  4  feet  0  inches  high  with 
a  space  below  them.  The  larger 
and  more  expensive  panels  have 
a  total  height  of  about  7  feet  6 
inches  running  down  to  the  floor 
and  are  provided  with  an  angle 
iron  or  pipe  frame.  For  the 
small  boards  the  frame  is  as 
shown  in  Fig.  177  made  of  verti- 
cal gas  pipe  one  at  each  end  of 
the  board  and  one  at  the  junc- 
tion line  of  adjacent  panels. 

Special  fittings  are  supplied  for  clamping  to  the  pipe  and  a 
continuous  flat  strap  3^  inch  X  1%  inch  in  section  running 
the  length  of  the  board  is  bolted  to  the  fittings  at  the 
top  of  the  pipe  to  stiffen  the  framework  and  to  provide  a  suit- 
able location  for  attaching  wall  braces,  transformers,  wiring, 
brackets,  etc.  The  lower  end  of  the  vertical  pipes  are  screwed 
into  ornamental  cast-iron  bases  which  can  be  bolted  to  the  floor. 


FIG.   177. — Pipe  framework  for 
switchboards. 


small 


SWITCHBOARDS— GENERAL  INFORMATION 


279 


These  bases  are  circular  and  can  be  screwed  on  or  off  a  short 
distance  to  allow  for  slight  irregularities  in  the  floor.  Special 
fittings  are  designed  for  clamping  to  the  upright  pipes  and  the 
panels  are  bolted  to  these  fittings.  The  entire  design  of  this 
frame  work  has  been  made  with  the  view  of  minimizing  the 
amount  of  machine  work  and  expediting  the  assembling  of  the 
frame.  For  small  boards  this  type  of  frame  has  proved  to  be 
very  satisfactory  and  a  complete  line  of  brackets  to  support  bus 
bars,  transformers,  fuse  blocks,  regulators,  etc.,  is  available. 

Pipe  Frame. — While  the  gas  pipe  construction  is  considerably 
lighter  than  the  angle  iron  construction  it  has  been  found  amply 
secure  for  these  smaller  switchboards  and  in  fact  some  manu- 
factures use  gas  pipe  construction  for  most  of  their  larger  switch- 
board installations.  Where  the 
number  of  panels  does  not  exceed 
four  or  five  the  complete  board 
can  sometimes  be  shipped  with 
the  panels  attached  to  the  frame- 
work and  most  of  the  small  wiring, 
etc.,  undisturbed  but  if  the  board  is 
a  large  one  the  panels  and  frame 
are  shipped  separately 

Angle  Frame. — For  the  larger  and 
more  expensive  panels  a  framework 
of  angle  iron  construction,  Fig.  178, 
is  used  by  certain  builders.  Each 
panel  of  a  total  height  of  90  inches 
is  provided  with  two  2  X  3  X 
24-inch  angle  irons  or  some  similar 
section  with  the  2-inch  side  next 
the  panel  and  these  angle  irons 
extend  from  the  bottom  of  the  panel 
to  within  ^  inch  of  the  top.  The 

vertical  angles  on  adjacent  panels  are  bolted  together  through 
the  3-inch  web  and  are  provided  with  corner  angles  for  bolting 
at  the  bottom  to  a  6  X  2-inch  channel  iron  forming  the  base  of 
the  frame  and  at  the  top  to  a  ^  X  1%-inch  flat  iron.  The  chan- 
nel iron  and  the  top  iron  are  made  continuous  and  the  entire 
length  of  the  board  provided  same  is  not  over  16  feet.  Where 
the  length  exceeds  this  amount  the  frame  is  divided  at  the 
junction  line  of  two  panels.  This  arrangement  makes  a  very 


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i 

i 

*, 

ji 

i 

*s-  „  „ 

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J>»'G 
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^art 

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r2"      *4 

4^"         -Hr- 

FIG.  178. — Angle    framework 
large  switchboards. 


for 


280        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

stiff  construction  and  the  channel  iron  base  makes  up  for  any 
irregularities  in  the  floor  and  distributes  the  weight  better  than 
a  framework,  where  no  channel  iron  base  is  furnished.  The  top 
provides  a  means  of  attaching  wall  braces,  brackets,  etc.  Some- 
times a  flat  soleplate  or  wooden  sill  is  provided  in  place  of  the 
channel  iron  base  or  the  vertical  angles  are  connected  directly 
to  the  floor. 

Shipment. — Each  panel  is  shipped  bolted  to  the  two  angle 
irons  that  form  its  individual  frame  and  this  obviates  any  neces- 
sity of  disconnecting  the  wiring  between  the  various  slabs  mak- 
ing up  the  panel.  The  framework  being  shipped  with  the  panels 
to  a  large  extent  reduces  the  breakage  due  to  rough  handling  and 
facilitates  the  erection  of  the  board  at  its  destination.  With  a 
pipe  framework  the  panels  and  uprights  must  be  shipped  sepa- 
rately, unless  a  temporary  upright  is  furnished  for  each  panel 
but  one. 

Material. — After  trying  various  materials  practically  all 
switchboard  builders  have  come  to  the  use  of  either  slate  or 
marble  although  in  a  few  instances  soapstone,  brick  or  steel  has 
been  used  but  these  cases  are  so  few  that  they  can  be  left  out 
of  consideration. 

Marble. — Marble  used  on  switchboards  is  usually  of  the  grade 
known  as  "Blue  Vermont,"  although  occasionally  "White  Ital- 
ian" or  "Pink  Tennessee"  is  used.  This  is  ordinarily  beveled 
with  a  45-degree  bevel  of  either  %  inch  or  ^  inch  measured  in  the 
plane  of  the  front  of  the  panel  or  its  edge  and  not  along  the  bevel. 
The  marble  is  sometimes  polished  on  the  front  face  and  bevels 
and  occasionally  the  edges  and  back.  Sometimes  the  marble  or 
slate  is  given  a  polished  black  enamel  finish  but  the  present 
standard  is  a  dull  black  marine  finish  applied  to  honed  panels  of 
marble  or  slate  of  any  color  or  an  oil  finish  applied  to  natural 
black  slate. 

Blue  Vermont. — The  name  "Blue  Vermont  Marble"  was  ori- 
ginally applied  to  the  marble  of  gray  or  bluish  tint  obtained  from 
the  quarries  of  the  Proctor  Blue  Vermont  Marble  Company  who 
supplied  most  of  this  grade  of  marble,  but  other  quarries  supply 
marble  of  practically  the  same  kind.  Polished  blue  Vermont 
marble  in  the  opinion  of  many  people  presents  a  somewhat  finer 
appearance  than  any  other  material  available  for  switchboards 
but  it  has  the  drawback  of  showing  oil  stains  and  scratches  and 
it  is  hard  to  secure  a  good  match  of  shade  and  grainings  for  large 


SWITCHBOARDS— GENERAL  INFORMATION  281 

switchboards.  The  difficulty  of  keeping  an  exact  record  of  the 
shades  and  markings  of  the  marble  shipped  to  a  certain  customer 
who  desires  additions  to  his  board  militates  somewhat  against 
its  use.  The  same  remarks  apply  to  English  vein,  white  Italian 
or  pink  Tennessee  marble. 

Slate. — Ordinary  slate  owing  to  its  irregular  color  and  marking 
is  seldom  used  in  its  natural  state  but  is  usually  given  an  enamel 
or  marine  finish,  while  natural  black  slate  is  given  an  oil  finish. 
Slate  can  be  given  a  baked  enamel  finish  of  glossy  black  and 
with  this  finish  oil  has  little  effect  and  there  is  no  difficulty  in 
securing  a  good  match.  This  finish  is  somewhat  more  expen- 
sive than  the  polished  and  has  the  same  drawback  of  showing 
scratches,  etc.,  which  cannot  well  be  removed  or  covered  over 
without  re-enameling.  As  this  involves  taking  the  panel  from 
the  board,  removing  all  apparatus  and  baking  the  panel,  this  is 
seldom  done.  When  a  black  enamel  finish  is  given  to  marble 
trouble  is  apt  to  come  from  the  marble  crumbling  during  the 
baking  process. 

Marine  Finish. — This  finish  as  applied  to  panels  of  either  slate 
or  marble  consists  of  a  dead  black  paint,  usually  applied  with  an 
atomizer  to  a  honed  finished  panel.  This  finish  is  cheap,  very 
attractive,  does  not  show  oil  stains,  and  if  the  panel  is  scratched 
a  little,  fresh  paint  will  make  it  look  as  good  as  new.  The  dull 
black  finish  moreover,  causes  the  instruments,  switches,  etc., 
to  stand  out  in  bold  relief  and  has  no  tendency  to  reflect  the 
light  in  the  eyes  of  the  attendant  while  polished  or  enameled 
panels  have  this  tendency. 

Oil  Finish. — When  natural  black  slate  is  used  it  is  given  an  oil 
finish  with  vaseline  or  some  similar  material  and  it  has  practi- 
cally the  same  advantages  as  the  marine  finish. 

Slate  vs.  Marble. — Where  switchboard  panels  are  to  be  given 
a  black  finish  the  question  of  whether  slate  or  marble  should  be 
used  is  largely  a  question  of  cost  of  insulation.  Slate  is  con- 
siderably cheaper  and  somewhat  stronger  than  marble  and  where 
the  voltage  of  live  metal  parts  mounted  on  the  panels  does  not 
exceed  750  volts  it  answers  just  as  well.  This  makes  it  suitable 
for  all  boards  except  those  having  ground  detector  receptacles, 
fuse  blocks  or  similar  apparatus  mounted  on  the  material  of  the 
panel  and  connected  to  a  circuit  of  1200  volts  or  more. 

Small  Panels. — The  smaller  and  cheaper  panels  intended  for 
use  with  gas  pipe  framework  are  made  in  single  slabs  and  as  a 


282        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

rule  have  a  height  of  48  inches  and  a  width  of  16  to  24  inches  al- 
though some  of  the  panels  are  smaller.  In  order  to  secure  suffi- 
cient mechanical  strength  to  stand  the  jar  of  oil  circuit  breaker 
opening,  the  panels  are  made  of  13^ -inch  thick  material  for 
alternating-current  service  and  panels  with  this  thickness  of 
1^2  inches  have  been  usually  adopted  as  standard. 

Bevels. — A  bevel  is  furnished  on  all  of  these  panels  to  improve 
their  appearance  and  also  because  it  is  almost  impossible  to 
secure  marble  or  slate  with  a  square  edge  that  will  stand  hand- 
ling. It  has,  in  fact,  been  found  advisable  to  use  a  small  bevel 
or  rounding  of  ^{Q  inch  or  %  inch  on  the  back  of  the  panel  to 
prevent  chipping  off. 

Early  Panels. — When  the  building  of  small  panel  boards 
for  A.C.  and  D.C.  work  was  begun  it  was  found  by  one  large 
manufacturer  that  a  height  of  48  inches  with  a  width  of  32 
inches  for  the  A.C.  panels  and  22  inches  for  the  D.C.  panels 
was  the  minimum  size  that  would  permit  the  mounting  of  all 
of  the  then  standard  apparatus  required  with  due  regard  to 
insulation  distances  and  the  lining  up  of  apparatus  on  generator 
and  feeder  panels  of  various  capacities  and  these  particular  sizes 
have  been  retained  as  standard. 

Frame.— -  Where  the  standard  frame  is  used  with  panels  48 
inches  high  the  bottom  of  the  panel  is  28%  inches  from  the  floor 
and  there  is  sufficient  clearance  to  allow  a  sub-panel  to  be  used. 
The  height  selected  for  the  frame  brings  the  meters  in  line  with 
the  operator's  eyes  and  places  the  switches,  rheostats,  etc.,  in  a 
convenient  location.  For  the  heavier  lines  of  panels,  2-inch  mar- 
ble or  slate  has  been  adopted  as  standard  for  mechanical  reasons. 
This  thickness  is  required  for  the  heavy  switches,  circuit  breakers, 
etc.,  often  furnished  on  these  switchboards.  These  2-inch  panels 
are  all  provided  with  a  %-inch  or  ^-inch  bevel  on  each  front  edge. 
With  three  division  panels  employing  slate,  the  thickness  is  fre- 
quently reduced  to  1%  inches. 

Westinghouse  Panel  Sections. — The  total  height  of  standard 
switchboard  panels  of  one  design,  viz.,  90  inches  from  the  channel 
iron  as  well  as  the  division  resulting  in  having  a  25-inch  lower 
slab  on  Westinghouse  boards,  is  due  to  the  fact  that  these 
particular  dimensions  were  best  adapted  to  the  line  of  switches, 
circuit  breakers,  meters,  etc.,  which  were  in  use  at  the  time  when 
the  standard  railway  switchboard  panels  shown  in  Fig.  179  were 
first  brought  out.  The  lower  25-inch  slab  was  used  for  the  rheo- 


SWITCHBOARDS— GENERAL  INFORM  A  TION 


283 


stat  faceplates  having  the  contacts  and  contact  mechanism  on 
the  rear  and  the  hand  wheels  on  the  front  of  the  panel.  In  order 
to  correspond  with  the  old  D.C.  panels,  the  A.C.  panels  were 
brought  out  having  a  main  slab  65  inches  high. 


Fio.  179. — Old  style  Westinghouse  two  section  switchboard. 

G.  E.  Panel  Sections. — While  the  Westinghouse  Company  was 
bringing  out  65-inch  X  25-inch  panels,  the  General  Electric 
Company  working  along  their  own  lines  and  designing  panels 
suitable  for  their  apparatus,  arrived  at  the  same  total  height,  but 
divided  their  panels  into  2  slabs  62-28  inches  high  with  a  %-inch 
bevel.  This  question  of  bevels  and  division  of  the  panels  is 
almost  entirely  a  question  of  appearance. 

Three  Section  Panels. — When  the  present  standard  laminated 
brush  type  carbon  break  circuit  breaker  was  designed,  it  was 
found  advisable  to  mount  this  breaker  at  the  top  of  the  panel  in 
order  to  take  advantage  of  the  tendency  of  an  arc  to  rise  and  to 
avoid  placing  apparatus  above  the  arc.  As  all  of  the  Westing- 
house  standard  breakers  up  to  3000-amperes  capacity  required  a 
space  of  something  less  than  20  inches,  they  soon  decided  to  divide 
the  main  upper  65-inch  panel  into  2  slabs,  one  portion  being  20 
inches  high  to  contain  the  circuit  breaker,  the  other  portion  45 
inches  high  to  contain  the  meters,  switches,  etc.  By  placing  the 
circuit  breaker  on  a  separate  slab,  the  calibration  of  the  breaker 
was  greatly  facilitated.  For  this  reason,  the  standard  D.C. 
panels  of  the  Westinghouse  Electric  &  Manufacturing  Company 
both  for  railway  work  and  for  light  and  power  work  were  divided 


284         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

into  3  slabs,  upper  20  inches  high,  the  middle  45  inches,  and  the 
lower  25  inches,  Fig.  180.  With  the  growth  in  the  capacity  of 
synchronous  converters,  larger  breakers  than  3000  amperes  became 
necessary,  and  these,  while  too  long  for  20-inch  slabs,  would  go  on 
25-inch  slabs  so  the  latest  Westinghouse  panel  division  is  25  inches, 
45  inches,  20  inches,  and  the  G.  E.  division  is  31  inches,  31  inches, 


FIG.   180. — Westinghouse  three  section  railway  switchboard. 

and  28  inches,  Fig.  181.  Nearly  all  switchboard  builders  are 
now  following  this  practice  of  putting  heavy  circuit-breakers  on 
separate  slabs.  Instruments  are  frequently  placed  below  the 
circuit  breakers  on  the  31-inch  upper  sections  of  G.E.  panels. 

Direct  Control. — Direct-control  switch  gear  is  used  with  practi- 
cally all  direct-current  plants  and  most  of  the  smaller  alternating 
ones  and  the  main  switching  appliances  are  located  directly  on 
the  switchboard  which  is  usually  of  the  panel  type.  Such  boards 
are  familiar  sights  in  moderate  size  plants. 


SWITCHBOARDS— GENERAL  INFORMATION 


285 


Many  Builders. — Owing  to  the  comparative  simplicity  of 
direct-control  switchboards  particularly  for  low  voltage  direct- 
current  service  the  number  of  builders  of  this  type  of  board  is 
very  large  and  the  consequent  competition  has  aided  greatly  in 
bringing  about  cheap  and  simple  apparatus  for  this  class  of 
service.  In  order  to  meet  close  competition  in  the  matter  of 
cost  and  promptness  of  delivery  nearly  all  switchboard  builders 
have  come  to  the  practice  of  using  so-called  "standard  panels" 
wherever  possible  and  very  complete  "lines"  of  standard  panels 

31- 


-28' 


•31 


\4-~20  -—  -  -S 

|<  ~—45  -> 

<  25"-  ->j 

rn 

flp 

2 

o 

p 

FIG.   181. — Three  section  panel. 

have  been  designed  to  take  care  of  all  ordinary  and  some  extra- 
ordinary features  that  are  apt  to  be  met  with  in  plants  of  moderate 
capacity  that  can  be  satisfactorily  handled  by  "direct-control 
switch  gear." 

Switchboards  can  be  obtained  to  meet  any  possible  require- 
ment that  may  arise  in  the  control  and  application  of  electrical 
power. 

Standard  Panels. — These  have  been  designed  using  standard 
apparatus  for  various  classes  of  services  and  these  panels  will  be 
found  to  meet  practically  all  ordinary  requirements  that  may 
come  up  in  switchboard  installations. 

Specials. — However,  for  special  conditions  that  cannot  be  met 
by  these  standard  panels,  or  where  special  material  is  desired, 


286         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

the  extensive  manufacturing  facilities  and  long  engineering 
experience  of  the  companies  insure  that  such  propositions  will 
be  taken  care  of  promptly  and  completely. 

Requirements. — The  selection  of  suitable  switchboard  ap- 
paratus for  certain  requirements  is  naturally  governed  by  several 
conditions.  In  some  cases  first  cost  is  the  determining  feature. 
In  most  cases  continuity  of  service  is  of  considerable  importance. 
In  many  cases  continuity  of  service  must  be  provided  regardless 
of  cost.  In  all  cases,  the  maximum  degree  of  safety  to  life  and 
property  that  can  be  obtained  should  be  the  goal.  These,  and 
other  considerations,  such  as  space  available,  voltage  and  capa- 
city of  plant,  govern  the  proper  selection  of  a  switchboard  equip- 
ment. 

With  regard  to  the  kind  of  current  controlled,  switchboards 
are  naturally  divided  into  two  broad  classes:  Direct-current 
switchboards  and  alternating- current  switchboards. 

D.C.  Boards. — The  direct-current  switchboards  cover  a  wide 
field  and  include  in  their  range  every  application  of  direct  current. 
In  general,  the  direct-current  panels  may  be  divided  into  two 
classes — those  of  the  larger  capacities,  and  those  of  the  smaller. 

The  larger  boards  are  used  for  direct  current  railway  systems 
and  for  lighting  and  power  systems  of  large  industrial  plants, 
hotels,  central  stations,  etc.  The  smaller  generator  and  feeder 
panels  are  intended  primarily  for  light  and  power  systems  of 
small  industrial  plants,  small  hotels  and  central  stations  of  small 
capacity,  etc.,  while  the  battery-charging  panels  are  designed 
for  controlling  the  charging  of  storage  batteries  used  in  lighting 
service  and  on  electric  vehicles. 

A.C.  Boards. — Alternating-current  switchboards  may  be  di- 
vided into  the  following  three  distinct  classes,  depending  on 
the  mounting  and  method  of  operation  of  the  apparatus: 

1.  Direct-control  boards,  or  those  in  which  all  apparatus  is 
mounted  on  the  panels  or  on  their  supporting  framework. 

2.  Manual   remote-control   boards,    or   those  with  manually 
operated  circuit  breakers  mounted  apart  from  the  board  and 
operated  by  means  of  handles  on  the  panels. 

3.  Electrical   remote-control  boards,   or  those  with    electri- 
cally operated  circuit  breakers  mounted  apart  from  the  board 
and  operated  by  means  of  control  switches  mounted  on  the 
panels. 

Class  of  Board. — The  particular  class  of  board  to  be  selected 


SWITCHBOARDS— GENERAL  INFORMATION  287 

for  any  installation  will  depend  on  a  number  of  considerations. 
For  instance,  the  capacity  of  the  station,  the  desired  operating 
features,  the  allowable  space,  the  permissible  cost — all  are  factors 
in  the  selection  of  the  proper  type  of  board. 

Limitations. — The  capacity  of  a  station  determines  the  class 
of  switching  devices  that  can  be  used,  and  this  in  turn  usually 
determines  the  class  of  switchboard  to  be  installed.  The  desired 
operating  features  are  a  factor  in  the  selection  of  either  me- 
chanically or  electrically  controlled  apparatus.  The  allowable 
space  may  determine  the  type  of  equipment.  The  direct-control 
switchboard  occupies  less  total  space  than  any  other,  but  some- 
times involves  more  valuable  space  in  the  operating  room  than 
the  remote-control,  hence  the  disposition  of  the  available  space 
sometimes  must  be  considered.  With  regard  to  cost,  the  direct- 
control  board  usually  costs  less  than  any  other,  although  the 
saving  in  main  cables,  may  sometimes  be  great  enough  with  the 
remote-control  boards  to  reduce  the  total  cost  of  cables  and 
switchboard  to  that  of  the  direct-control,  or  to  even  less. 

Direct  Control. — The  limitations  in  the  use  of  the  direct-con- 
trol switchboards  are  chiefly  electrical.  Experience  has  demon- 
strated that  there  are  certain  limits  of  capacity  above  which  oil 
circuit  breakers  should  not  be  mounted  directly  on  the  panels. 
The  reason  for  this  limitation  lies  chiefly  in  the  danger  to  at- 
tendants from  high  voltage  apparatus  when  in  close  proximity 
to  low  voltage  control  and  instrument  wiring,  rheostats,  etc., 
which  require  inspection  and  occasional  repairs,  or  from  mechani- 
cal reasons  resulting  from  the  size  and  amount  of  copper  busses 
and  risers  when  the  current  involved  exceeds  certain  amounts. 

Remote  Control. — Manual  remote-control  switchboards  are 
limited  in  their  application  by  the  physical,  rather  than  the  elec- 
trical, characteristics.  They  are  applicable  where  the  simplicity 
of  connections  or  accessibility  desired  cannot  be  obtained  with 
panel  mounted  apparatus,  where  station  capacity  or  voltage  is. 
so  high  as  to  make  it  desirable  to  mount  oil  circuit  breakers  apart 
from  the  panels,  and  where  station  arrangement  permits  the  use  of 
manually  operated  remote  controlled  oil  circuit  breakers. 

Electrical  Control. — The  electrical  control  switchboard  usually 
takes  one  of  three  general  forms,  namely :  the  panel  board,  the 
combination  control  desk  and  elevated  instrument  board,  or 
the  combination  pedestal  and  instrument  post  board.  All 
of  these  are  detailed  later. 


288         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Panels. — As  in  the  application  of  the  other  types  of  boards 
there  is  no  well  denned  field  to  which  any  of  the  three  forms  is 
confined.  However,  the  panel  board  is  frequently  chosen  for 
plants  of  moderate  capacity,  and,  occasionally,  for  those  of  high 
capacity  where  the  number  of  circuits  are  few  and  the  length  of 
the  board  is,  kept  therefore  within  a  space  which  may  be  covered 
almost  instantly  by  the  operator.  The  panel  board  is  usually 
chosen  for  substations,  as  it  must  generally  harmonize  with,  and 
may  be  an  addition  to,  the  panel  board  controlling  the  direct- 
current  and  low  tension  alternating-current  circuits. 

Desks. — The  combination  control  desk  and  elevated  instru- 
ment board  can  be  used  for  stations  of  any  capacity  and  any 
number  of  circuits.  The  particular  form  chosen,  however,  must 
depend  upon  local  conditions,  but  in  general,  for  a  small  number 
of  circuits,  the  linear  desk  is  employed,  while  for  a  greater 
number  of  circuits,  the  semi-circular  desk  is  most  desirable  as  it 
permits  a  uniform  view  of  all  sections  of  the  desk  from  one 
central  position. 

Pedestals. — When  a  station  is  equipped  with  very  large  units, 
pedestals  for  the  control  switches  and  receptacles,  with  posts  for 
supporting  the  instruments,  are  sometimes  used  because  of  the 
complete  individuality  thus  obtained  for  each  unit. 

On  remote-control  boards  all  busses  and  connections  are  shipped 
in  bulk  uncut.  On  panel  mounted  boards,  if  bus  bars  and  con- 
nections are  of  strap,  rod,  or  tubing,  they  are  cut,  bent  and  put  in 
place;  if  they  are  of  solid  insulated  wire  they  are  shipped  in  reels, 
uncut,  together  with  the  wire  for  control  and  instrument  busses 
and  for  primary  leads  of  voltage  transformers. 

Panel  Sequence. — The  sequence  of  panels  is  important  on 
account  of  the  necessity  for  designing  a  switchboard  to  provide 
for  future  extensions,  for  the  most  economical  distribution  of  bus 
bar  copper,  and  to  provide  means  for  measuring  the  total  load. 

When  a  switchboard  comprises  generator,  totalizing,  and 
feeder  panels  only,  the  standard  arrangement  of  panels  when 
facing  the  front  of  the  switchboard  is  to  place  the  generator  panels 
at  the  left,  the  feeder  panels  on  the  right,  and  the  load  or  instru- 
ment panels  between  the  two. 

Bus  Taper. — In  fixing  any  arrangement  of  panels  it  is  most 
practical  and  economical  to  locate  the  heaviest  capacity  panels 
next  to  the  totalizing  panels,  the  lightest  capacity  panels  being 
located  at  the  ends.  The  bus  bar  copper  can  then  be  tapered  by 


SWITCH  BO  A  HIM—GENERAL  INFORM  A  TION 


289 


the  use  of  laminated  bus  bars.  This  construction  reduces  the 
amount  of  bus  bar  copper  to  a  minimum  and  permits  making 
extensions  easily.  A  typical  layout  is  shown  in  Fig.  182. 

Location. — In  many  cases  control  apparatus  and  switching 
devices  can  be  located  to  advantage  near  the  machines  controlled 
and  save  great  expense  in  ducts  and  conductors,  and  avoid  un- 
necessary complications.  Such  devices  can  be  made  electrically 
operated  if  the  control  is  to  be  concentrated  on  one  main  switch- 
board. 


These //gvres  rtyresef>rB</s 

Bar  eapoc/fy 

po/nfs  /nc//r.0/ptf6y 

wrt/cfi  represent  //>epo/nfsa/ 

i  ftotver 
Bus 


These  //gvrts  represent 


t>ff*err>  po/nfs  /nt/tcafe* 
ty  ffrrotv  /tetK/s  rvri/cri  rf- 
preseri  r/fte  p&n  fs 
ft>MVr  /s  foAen/rorn  fft/f 


600       601 


Fia.   182. — Typical  bus  bar  tapering. 

Copper. — The  most  economical  distribution  of  conducting 
copper  is  frequently  possible  with  remote  controlled  switching 
devices  since  the  switching  apparatus  can  be  located  to  the  best 
advantage  without  reference  to  the  location  or  width  of  panels. 

The  amount  of  bus  copper  required  for  a  switchboard  equip- 
ment depends  on  the  arrangement  of  panels  and  the  distribution 
of  circuits. 

The  amperes  allowable  per  strap  in  the  bus  bar  will  vary  ac- 
cording to  the  conditions  of  installation  and  service.  The  shape 
and  dimensions  of  conductors,  the  relative  position  of  conduc- 
tors, and,  in  the  case  of  alternating  current,  the  frequency,  all 
contribute  to  fix  the  effective  capacity  of  a  single  strap  in  any 
given  installation. 

Carrying  Capacity. — For  alternating-current  switchboards 
for  capacities  requiring  but  one  strap,  a  2-inch  X  3^-inch  strap 
will  carry  550  amperes  and  a  3-inch  X  M-inch  strap  will  carry 
850  amperes  at  frequencies  not  greater  than  60  cycles.  For  bus 
capacities  above  2500  amperes,  60  cycle,  or  4000  amperes,  25 
cycle,  careful  designing  is  needed  to  secure  the  proper  bus  bar 
layout.  In  general,  for  bus  capacities  above  the  values  given, 


290     •    SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

the  maximum  temperature  rise  of  the  copper  will  exceed  28 
degrees  Centigrade,  due  to  unequal  distribution  of  current  in  the 
busses,  since  the  inductive  effect  of  adjacent  busses  causes  increase 
in  current  density  on  one  side  of  the  respective  bus  bars  and 
produces  unequal  heating  of  the  straps  forming  the  bus.  Inter- 
lacing of  phases  or  special  arrangements  of  conductors  can  some- 
times be  adopted  to  secure  a  balance  of  the  mutual  inductive 
effects,  better  current  distribution  and  more  efficient  use  of  the 
copper. 

Exciter  Bus. — Exciter  bus  bars  ordinarily  extend  across  the 
exciter  panels  and  the  alternating-current  generator  panels ;  and  if 
used  exclusively  for  the  exciting  current,  their  capacity  need  not 
exceed  the  total  current  required  by  the  generator  fields.  The 
standard  exciter  bus  bars  for  capacities  up  to  400  amperes  is  one 
2-inch  X  J^-inch  copper  strap;  up  to  600  amperes,  one  3-inch  X 
2^-inch  strap;  up  to  800  amperes,  one  3-inch  X  34 -inch  strap  and 
up  to  1200  amperes,  two  3-inch  X  K-inch  straps. 

Equalizer  Bus. — The  cross-section  of  the  equalizer  bus  bar  is 
in  general  made  about  one-half  that  of  the  positive  or  negative 
bus  behind  the  generator  panels. 

Copper  Sizes. — 3-inch  X  ^-inch  copper  strap  can  be  used  to 
advantage  for  bus  bar  capacities  up  to  4000  amperes.  6-inch 
X  H-inch  copper  strap  can  be  used  to  advantage  for  bus  bar 
capacities  above  4000  amperes  up  to  8000  amperes,  10-inch  X 
34-inch  copper  strap  for  bus  bar  capacities  above  8000  amperes. 

Ultimate  Bus  Capacity. — In  designing  a  switchboard,  an  esti- 
mate should  be  made  regarding  the  probable  ultimate  continuous 
bus  capacity  so  that  straps  of  proper  dimensions  and  proper  bus 
structures  or  supports  can  be  utilized  to  take  care  of  probable 
future  additions. 

In  cases  where  the  load  is  a  fluctuating  one,  or  the  load  factor 
is  low,  as  in  a  synchronous  converter  substation  of  an  interurban 
railroad  the  section  of  the  bus  can  sometimes  be  safely  reduced 
below  that  figured  from  the  usual  table. 

Tubing — Carrying  Capacity. — In  high  tension  layouts,  22,000 
volts  and  over,  the  connections  and  bus  bars  frequently  consist  of 
brass  or  copper  tubing,  iron  pipe  sizes.  This  tubing  in  standard 
lengths  can  be  furnished  on  order  when  required. 

The  carrying  capacities  given  below  are  based  on  a  tempera- 
ture rise  of  28  degrees  Centigrade.  The  sizes  are  iron  pipe  sizes. 

For  connections  of  moderate  length,  the  capacity  of  1^4 -inch 


SWITCHBOARDS— GENERAL  INFORMATION 


291 


copper  tubing  may  be  increased  to  800  amperes,  other  sizes  in 
proportion. 


Size  of  pipe, 

Area  in 

Amperes 

inches 

circular  mils 

Copper  bus 

Brass  bus* 

Iron  busf 

H 

314,975 

250 

50 

30 

H 

426,816 

350 

70 

42 

i 

601,381 

500 

100 

60 

IK 

884,176 

725 

145 

87 

*20  per  cent,  conductivity. 


fl2  per  cent,  conductivity. 


Panel  Ratings. — The  ampere  rating  of  a  switchboard  panel 
corresponds  to  the  capacity  of  the  switches  or  circuit  breakers 
mounted  on  the  panel  or  controlled  from  it.  The  switches  and 
circuit  breakers  are  rated  in  accordance  with  the  National  Elec- 
trical Code  and  will  carry  their  rated  current  continuously. 

Switches  and  circuit  breakers  are  given  a  maximum  rating  as 
they  reach  a  final  temperature  quickly  when  carrying  a  steady 
current.  Their  capacity  must,  therefore,  correspond  to  the  one 
or  two-hour  overload  capacity  of  the  machine  or  circuit,  if  such 
a  rating  exists,  in  addition  to  its  continuous  capacity. 

Temperature  Rise. — The  usual  temperature  rise  guarantee 
for  switchboard  apparatus  when  carrying  its  rated  current  is  28 
degrees  Centigrade  for  knife  switches,  30  degrees  Centigrade  for 
conducting  parts  of  carbon  and  oil  circuit  breakers,  and  50  degrees 
Centigrade  for  circuit-breaker  coils  and  frames.  Bus  bars  and 
connections  are  proportioned  so  as  not  to  exceed  28  degrees  Centi- 
grade rise  and  instrument  transformers  are  not  allowed  to  exceed 
50  degrees  Centigrade.  Shunts  and  resistances  are  exempt  from 
temperature  limitations.  A  room  temperature  of  40  degrees 
Centigrade  is  used  as  a  basis.  Where  the  room  temperature  ex- 
ceeds this  value,  larger  capacity  apparatus  should  be  chosen  in 
order  that  the  ultimate  temperature  will  not  exceed  those  fixed  on 
this  basis. 

The  maximum  possible  setting  of  overload  circuit  breakers 
should  not  be  less  than  the  momentary  overload  capacity  of 
the  machine  or  circuit. 

Ammeter  Scales. — Ammeters  are  commonly  furnished  with 
full  scales  corresponding  to  approximately  125  to  150  per  cent,  of 


292         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

the  ampere  rating  of  the  panel.  This  allows  for  overload  swings 
and  yet  gives  good  readability  of  scale  at  normal  load.  For 
railway  service,  D.C.  ammeters  are  furnished  with  scales  for  the 
momentary  overload  capacity  of  the  machine. 

Switching  Apparatus. — The  switching  apparatus  on  direct- 
current  circuits  consists  of  knife  switches  and  carbon  circuit 
breakers.  Oil  circuit  breakers  are  not  applied  on  D.C.  circuits, 
as  the  breaking  distances  are  proportioned  for  alternating  current 
and  are  not  great  enough  for  direct  current.  In  an  A.C.  circuit 
the  current  goes  to  zero  with  every  alternation,  thus  assisting 
in  breaking.  The  direct- current  arc  has  a  greater  volume  for  the 
same  current,  and,  besides  requiring  greater  distances  and  oil 
volumes,  the  oil  carbonizes  much  more  rapidly,  thus  impairing 
its  insulating  value. 

Oil  Breakers. — Non-automatic  oil  circuit  breakers  can  be  used 
on  standard  high  voltage  direct- current  arc  lighting  panels  where 
the  circuit  is  not  over  10  amperes,  and  where  the  breakers  are 
always  opened  by  hand  and  then  only  infrequently.  The  recti- 
fier arc  regulators  are  commonly  disconnected  by  opening  the 
A.C.  primary  breaker  first  so  that  the  D.C.  secondary  breaker  need 
not  be  opened  under  load.  Oil  circuit  breakers  are  used  princi- 
pally for  the  control  of  alternating  current,  and,  hence,  find  their 
greatest  application  in  connection  with  A.C.  switchboards. 

Ratings. — They  are  rated  as  to  voltage,  amperage,  frequency, 
interrupting  capacity  and  instantaneous  current- carry  ing  ca- 
pacity. The  voltage  rating  is  the  maximum  voltage  at  which  the 
breaker  may  be  used  and  still  meet  standard  A.I.E.E.  rules 
on  voltage  tests.  If  the  nominal  voltage  of  the  system  equals 
the  breaker  voltage  rating,  which  is  a  maximum,  then  in  general 
the  next  higher  voltage  breaker  should  be  used.  The  ampere 
rating  is  the  maximum  current  for  its  guaranteed  temperature 
rise. 

Interrupting  Capacity. — The  ampere  interrupting  capacity 
of  a  circuit  breaker  is  the  highest  current  which  it  will  open  at 
any  specified  normal  voltage,  frequency,  and  duty.  This  ca- 
pacity depends  on  the  construction  of  the  breaker.  The  duty 
on  which  ampere  interrupting  values  are  based  assumes  that  the 
breaker  will  interrupt  a  circuit  twice  in  succession  at  an  interval 
of  2  minutes  and  then  be  able  to  carry  its  normal  current  until 
such  time  as  it  is  convenient  to  inspect  it  and  make  necessary 
adjustments. 


SWITCHBOARDS— GENERAL  INFORMATION  293 

In  order  to  protect  the  circuits  controlled  by  a  switchboard 
from  damage  due  to  sudden  overloads  some  device  may  be  con- 
nected in  the  circuit  that  will  automatically  break  it  when  an 
overload  is  applied.  The  devices  used  are  fuses  or  automatic 
carbon  or  oil  circuit  breakers,  depending  on  the  nature  of  the  cir- 
cuit or  apparatus  to  be  protected. 

Meter  Equipment. — The  selection  of  the  proper  meter  equip- 
ment for  a  switchboard  depends  on  the  class  of  board  employed, 
the  number  of  lines  controlled,  etc.  In  general,  a  careful  selec- 
tion of  suitable  meters  is  of  more  importance  on  the  larger  boards, 
especially  the  electrically  operated,  than  on  the  smaller  ones, 
for  the  reason  that  many  more  economies  can  be  introduced  in 
the  operation  of  a  large  station  by  skilled  operators  with  a  suitable 
meter  equipment  than  would  be  possible  in  a  smaller  plant.  On 
all  boards,  a  multiplicity  of  meters  should  be  avoided  and  only 
those  necessary  to  give  the  information  desired  should  be  used. 

D.C.  Meters. — On  D.C.  switchboards,  the  meter  equipment 
is  usually  quite  simple,  consisting  generally  of  one  voltmeter 
arranged  for  switching  to  each  generator  circuit,  one  ammeter 
for  each  generator  circuit,  and  an  ammeter  only  for  the  feeder 
circuits  except  in  cases  where  feeders  may  be  energized  from  an 
outside  source,  when  provision  should  be  made  for  reading  the 
feeder  voltage.  On  the  smaller  boards,  the  ammeter  may  be 
dispensed  with  on  the  feeder  panels. 

A.C.  Meters. — When  the  load  is  not  always  balanced,  alter- 
nating-current generators  should  be  equipped  with  an  ammeter 
in  each  phase,  or  with  one  ammeter  and  a  polyphase  ammeter 
switch  if  simultaneous  readings  are  not  desired.  In  case  the 
load  is  always  balanced,  a  single  ammeter  is  all  that  is  necessary. 

If  generators  operate  in  parallel  they  should  have  an  indicat- 
ing wattmeter  and  a  field  ammeter  in  addition  to  the  main  am- 
meter. If  cost  is  a  serious  consideration,  either  one  may  be 
omitted  but  not  both. 

Indicating  Wattmeter. — This  will  indicate  the  total  instanta- 
neous energy  load  on  the  machine  regardless  of  power  factor  or 
distribution  of  load.  Two  machines  of  the  same  size  operating 
in  parallel  may  have  the  same  curent  output,  but,  through  im- 
proper field  adjustment  one  machine  may  be  supplying  all  the 
load  or  even  driving  the  other  machine  as  a  motor,  without  the 
ammeters  indicating  any  abnormal  condition. 

Field  Ammeter. — This  serves  to  indicate  the  proper  adjust- 


294         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

ment  of  field  current  so  that  windings  will  not  be  overloaded. 
It  is  also  convenient  as  a  means  of  determining  the  cause  of  any 
abnormal  conditions  in  the  generator. 

Power  factor  meters  or  reactive  factor  meters  may  be  used  in 
addition  to,  or  in  place  of,  indicating  wattmeters,  but  a  com- 
parison of  the  wattmeter  reading  with  the  corresponding  readings 
of  the  voltmeter  and  ammeter  will  give  a  general  indication  of 
machine  power  factor. 

Bracket  Instruments. — Voltage  readings  of  machines  in  paral- 
lel are  usually  taken  by  means  of  a  "machine"  voltmeter  (which 
is  usually  mounted  on  a  swinging  bracket)  connected  to  volt- 
meter switches  on  the  individual  panels.  Most  operators  desire 
a  second  voltmeter  mounted  on  the  same  bracket  with  the  ma- 
chine voltmeter  and  connected  permanently  to  the  bus  bars. 
This  arrangement  permits  a  simultaneous  comparison  of  the 
bus  bar  and  machine  voltages  when  synchronizing. 

A  synchronoscope,  mounted  on  a  swinging  bracket,  for  indi- 
cating synchronism  when  connecting  an  incoming  machine  to 
the  bus  bars,  usually  forms  part  of  the  equipment.  This  instru- 
ment is  often  supplemented  with  two  110-volt  indicating  lamps, 
connected  to  be  dark  at  synchronism,  to  be  used  as  a  check  and 
as  a  reserve  in  case  the  synchronoscope  is  removed  temporarily. 
A  machine  or  bus  frequency  meter  is  frequently  advantageous. 

Feeders. — Alternating-current  feeder  circuits  are  usually  sup- 
plied with  ammeters  as  a  general  indication  of  the  feeder  load. 
Other  meters  such  as  frequency  meters,  power  factor  meters, 
indicating  wattmeters,  watt-hour  meters,  etc.,  are  supplied  ac- 
cording to  the  requirements  of  each  particular  case. 

Ground  Detectors. — Ungrounded  systems  should  be  equipped 
with  some  form  of  ground  detector  for  indicating  grounded  cir- 
cuits. For  systems  up  to  and  including  600  volts,  the  ground 
detector  usually  consists  of  incandescent  lamps  capable  of  with- 
standing full  bus  bar  voltage,  connected  in  series  from  each  bus 
bar  to  ground,  so  as  to  form  a  continuously  indicating  detector. 

For  2200  volts  and  above,  static  ground  detectors  may  be 
used.  These  are  operated  from  condensers  or  resistors  connected 
to  the  bus  bars  in  order  to  obviate  danger  from  high  voltage  in 
the  instrument.  The  detectors  must  be  rigidly  mounted  so  that 
the  position  of  the  leads  cannot  be  changed. 

Rheostats. — Field  rheostats  are  usually  operated  by  means  of 
a  handwheel  on  the  front  of  the  panel,  from  which  a  shaft  ex- 


SWITCHBOARDS— GENERAL  INFORMATION  295 

tends  through  the  panel  to  the  rheostat,  or  to  a  sprocket  for 
remote  control. 

Rheostats  that  are  sufficiently  small,  such  as  exciter  field  rheo- 
stats and  voltage  limiting  rheostats,  may  be  supported  on  a  tet- 
rapod  mounting  on  the  rear  of  the  board  immediately  back  of 
the  handwheel  and  operated  directly  through  the  shaft. 

In  practically  all  cases,  however,  generator  field  rheostats 
should  be  mounted  apart  from  the  switchboard  and  operated 
through  a  sprocket-and-chain  transmission  except  where  elec- 
trical operation  is  desired.  The  faceplates  are  usually  mounted 
directly  on  the  resistance  frames  and  wired  completely  before 
shipment.  When  individual  exciters  are  used  with  the  genera- 
tors, the  exciter  field  rheostat  may  be  mounted  in  combination 
with  the  generator  field  rheostat.  With  this  mounting,  the 
handwheels  and  shafts  for  the  two  rheostats  are  mounted  con- 
centrically, the  main  rheostat  being  controlled  through  the  outer 
shaft  and  the  exciter  rheostat  through  the  inner  shaft. 

Safety  Code. — On  account  of  the  general  adoption  of  the  Na- 
tional Safety  Code  either  as  a  legal  requirement  or  as  a  standard 
of  reference  in  courts  of  law  in  many  states,  with  the  probability 
that  it  may  become  the  basis  on  which  all  safeguards  against 
accident  or  damage  to  persons  are  provided,  it  is  recommended 
that  the  Code  be  taken  into  account  in  the  application,  installa- 
tion and  operation  of  the  switchboard  apparatus.  In  general, 
the  purchaser  should  provide  a  competent  operator  and  such 
guards,  shields,  insulating  mats,  isolation,  warnings,  and  other 
requirements  to  make  the  installation  comply  with  the  Code  as 
may  be  recommended,  unless  he  does  otherwise  at  his  own  risk. 


CHAPTER  XII 


SMALL  D.C.  &  A.C.  SWITCHBOARDS 

For  small  industrial  plants,  hotels,  garages,  etc.,  switchboards 
with  panels  48  inches  high  or  less  mounted  on  light  pipe  frame- 
work are  built  by  various  manufacturers.  While  the  practice 
of  the  different  builders  naturally  varies,  the  descriptions  that 
follow  may  be  taken  as  fairly  representative  of  this  class. 

BATTERY  CHARGING  PANELS 

Sectional  Type. — The  sectional  type  of  battery- charging 
panels  on  single  frame  shown  in  Fig.  183  are  designed  primarily 


FIQ.  183. — Sectional  type  of  battery  charging  board. 

for  use  in  public  and  private  garages  where  electric  vehicles  will 
be  charged.  The  charging  rheostats  specified  are  designed  for 
charging  batteries  recommended  by  the  Society  of  Automotive 

296 


SMALL  D.C.  AND  A.C.  SWITCHBOARDS  297 

Engineers,  namely,  40  to  44  cells  for  lead  batteries  and  60  to  62 
cells  for  Edison  batteries. 

Each  panel  consists  of  three  or  more  sections,  together  with 
charging  rheostats.  This  sectional  construction  provides  a 
large  variety  of  combinations,  thus  making  an  installation  very 
flexible,  as  the  number  of  charging  circuits  may  be  increased  at 
any  time  after  the  switchboard  has  been  installed,  by  the  addi- 
tion of  suitable  sections  and  rheostats. 

Rheostat. — Each  battery-charging  rheostat  consists  of  a  resist- 
or of  cast-iron  grids  supported  on  the  rear  of  each  panel  section 
between  steel  end  frames  with  contact  buttons  and  moving  arm 
on  the  front  of  the  panel  section.  Bolts  through  the  panel  hold 
the  end  frames  of  each  charging  rheostat  to  the  panels  so  that 
the  rheostat  forms  an  integral  part  of  the  section  equipment. 
By  disconnecting  the  wires  connecting  the  grids  to  the  contact 
button  terminals,  the  resistor  can  be  easily  removed  from  the 
panel. 

Assembly. — The  sections  of  each  panel  are  assembled  one 
above  another  and  securely  bolted  to  a  vertical  angle  iron  frame 
of  suitable  height.  The  simplest  panel  consists  of  one  or  more 
charging  sections  and  a  power  control  section  mounted  above  the 
charging  sections.  Swinging  brackets  at  the  side  of  the  panel 
will  mount  the  power  section  ammeter,  if  used,  and  the  battery- 
voltmeter  and  ammeter.  It  is  not  advisable  to  use  panels  ex- 
ceeding 90  inches  in  height,  because  some  of  the  switching  ap- 
paratus would  be  inconveniently  high  for  the  operator,  and, 
therefore,  when  more  sections  are  required  than  can  be  mounted 
on  a  frame  90  inches  high,  they  may  be  arranged  in  two  or  more 
panels  of  uniform  height.  Where  the  number  of  necessary  sec- 
tions is  not  sufficient  to  make  all  panels  the  same  height,  blank 
sections  may  be  provided  for  some  of  the  panels. 

Generator  Section. — Every  switchboard  or  panel  which  con- 
trols one  or  more  direct-current  generators  must  be  equipped 
with  an  individual  power  control  section  for  each  generator.  If 
generators  are  compound  wound  and  generator  control  sections 
with  circuit-breaker  protection  are  used  then  one  side  of  the 
generator  switch  will  be  connected  to  the  equalizer  bars,  the 
other  side  to  the  negative  bus,  and  the  circuit-breaker  will  be 
connected  in  the  positive  lead.  If  generator  control  section 
provides  fuse  protection  only,  then  an  equalizer  switch  must  be 
provided. 


298         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Locations. — A  rule,  incorporated  in  the  National  Electric  Code, 
specifies  that  charging  panels  located  in  garages  where  gasoline 
is  handled  must  have  all  spark  producing  devices  mounted  4 
feet  or  more  above  the  floor.  If  such  devices  are  mounted  less 
than  4  feet  above  the  floor,  the  charging  panel  must  be  surrounded 
by  a  vapor-proof  enclosure,  unless  the  panel  is  located  in  a  room 
or  enclosure  provided  for  this  purpose. 

Platform. — Switchboards  or  panels  controlling  several  charging 
circuits  will  regularly  have  the  switching  apparatus  mounted  less 
than  4  feet  above  the  floor  and  the  purchaser  is  expected  to  install 
the  panels  as  provided  for  by  the  Code.  In  most  cases,  the 
simplest  method  is  to  mount  the  board  on  a  concrete  platform 
4  feet  high. 

Protection. — The  arrangement  of  the  panel  sections,  and  com- 
bination of  them,  is  such  as  to  provide  a  maximum  of  protection 
to  the  operator.  Power  control  sections  employing  carbon  circuit 
breakers  will  be  located  at  the  top  of  the  panel.  The  contactors 
on  the  charging  sections  are  provided  with  blowout  coil  and 
shields.  The  operator  is  thus  protected  against  possible  injury 
due  to  moving  parts  or  to  the  arcing  of  automatic  devices. 

The  various  sections  are  made  up  of  slabs  1  inch  thick, 
K-inch  bevel.  These  sections  are  of  two  heights,  14  inches 
and  28  inches,  depending  upon  the  apparatus  mounted  on  the 
section. 

Ampere-hour  Meter  Sections. — These  are  equipped  with 
ampere-hour  meters  of  the  auto  type,  with  a  zero  contact  reset 
device  and  variable  resistor  element.  The  meter  is  designed  so 
that  it  will  run  "slow,"  when  the  charging  current  of  a  battery 
passes  through  it,  the  speed  being  adjustable  to  approximately 
compensate  for  the  charging  efficiency  of  any  battery.  When  a 
given  number  of  ampere  hours  for  which  the  meter  has  been  set 
have  been  supplied  to  the  battery,  the  pointer  will  again  be  at 
the  zero  position  and  will  close  the  zero  cont  act.  This  will  cause  the 
contactor  in  the  circuit  to  open,  thus  terminating  the  charge. 
Therefore,  to  charge  a  battery,  it  is  only  necessary  to  set  the  meter 
pointer  at  the  ampere  hours,  as  previously  discharged  from  the 
battery,  and  when  this  number  of  ampere  hours  (automatically 
corrected  for  charging  efficiency  by  the  resistor  element  of  the 
meter)  have  been  returned  to  the  battery  it  will  be  automatically 
disconnected. 

When  ampere-hour  meter  sections  are  used,  for  the  purpose  of 


SMALL  D.C.  AND  A.C.  SWITCHBOARDS  299 

automatically  terminating  the  charge  of  a  battery,  it  is  neces- 
sary to  use  charging  sections,  employing  a  contactor. 

Rheostats. — Each  power  control  section  to  be  used  for  the 
control  of  a  direct-current  generator  is  drilled  for  a  field  rheostat 
mounting  of  the  switchboard  type. 

Each  switchboard  that  controls  a  source  of  power  such  as  a 
direct-current  generator  must  be  equipped  with  a  ground  detector 
outfit.  For  such  panels,  two  110- volt  incandescent  lamps  are 
furnished  and  are  mounted  with  the  generator  ammeter  on  the 
swinging  bracket.  Each  of  the  lamps  is  connected  between  one 
side  of  the  line  and  ground,  thus  forming  a  continuous  indicator. 
Under  normal  conditions  each  lamp  will  glow  red  due  to  the  fact 
that  it  is  operating  on  about  one-half  normal  voltage.  If  the 
positive  line  becomes  grounded,  the  lamp  connected  to  that  line 
will  grow  dim  or  cease  to  glow  at  all,  while  the  other  lamp  will  in- 
crease in  brilliancy.  If  the  negative  side  is  grounded,  the  order 
of  brilliancy  is  reversed.  When  power  is  received  from  incoming 
direct-current  lines  the  lamps  are  not  required. 

Overload  Protection. — Plain  overload  protection  is  regularly 
furnished  for  all  sections.  For  this  purpose  there  is  furnished  for 
each  charging  circuit  a  National  Electrical  Code  fuse  holder  and 
enclosed  fuse  for  each  side  of  the  circuit. 

To  protect  the  battery  ammeter  against  overload,  a  fuse  is 
provided  and  is  connected  between  the  battery  ammeter  bus  bar 
and  the  main  negative  bus  bar.  This  fuse  is  regularly  mounted 
on  a  bracket  on  the  rear  of  the  panel. 

When  it  is  desired  to  use  two  or  more  battery  ammeters  inde- 
pendently, each  ammeter  must  be  protected  by  its  own  fuse. 

If  each  charging  circuit  is  to  be  protected  against  reversal  of 
current,  it  is  necessary  to  select  charging  sections  and  power  con- 
trol sections  for  this  service. 

Power  Control. — Power  control  sections  with  circuit  breaker 
protection  are  regularly  furnished  with  a  low  voltage  release  me- 
chanism attached  to  each  circuit  breaker  to  protect  the  source 
of  power  against  reversal  of  current.  When  this  circuit  breaker 
opens,  due  to  reversal  of  current,  the  auxiliary  contacts  with 
which  the  circuit  breaker  is  supplied  will  open  all  charging  cir- 
cuits which  are  provided  with  magnetically  operated  switches. 

In  case  power  control  sections  equipped  with  fuse  switch  pro- 
tection and  with  low  voltage  relay  switch  are  used,  the  reversal 
of  current  will  cause  the  low  voltage  relay  switch  to  open  and 


300         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

thereby  open  all  the  charging  circuits,  if  charging  sections  with 
contactors  are  used. 

Low  Voltage. — The  low  voltage  coil  of  the  carbon  circuit 
breaker  and  of  the  low  voltage  relay  switch  will  be  suitable  for 
115  volts  D.C.  In  case  the  generators  are  driven  by  A.C.  in- 
duction motors,  it  is  possible  to  obtain  A.C.  low  voltage  coils, 
so  that  on  failure  of  the  A.C.  power  the  low  voltage  relay  switch 
and  carbon  circuit  breaker  will  be  tripped. 

Reversal. — However,  when  several  generators  operate  in 
parallel  and  obtain  their  power  from  separate  sources  it  will  be 
necessary  to  use  reverse  current  relays,  in  order  to  insure'absolute 
protection  against  the  occurrences  of  reverse  current. 

From  the  battery  standpoint,  it  is  very  desirable  to  have  bat- 
tery circuits  protected  against  reverse  current.  If  only  the  gen- 
erator or  main  circuit  is  protected  against  reverse  current,  the 
batteries  remain  connected  in  parallel  to  the  bus  bars  (after  the 
circuit  breaker  opens).  Therefore,  the  batteries  having  the  high- 
est terminal  voltage  will  discharge  into  the  other  batteries  con- 
nected to  the  system. 

Reverse  Protection. — The  use  of  the  low  voltage  release  me- 
chanism, as  part  of  the  circuit  breaker  equipment,  or  the  use  of 
the  low  voltage  relay  switch,  is  adaptable  for  protection  against 
the  reversal  of  current  from  a  storage  battery,  because  at  ordi- 
nary temperatures  (from  60  degrees  to  90  degrees  Fahrenheit)  the 
voltage  of  a  good  battery  discharging  at  the  normal  rate  is  always 
lower  than  the  minimum  voltage  required  to  start  the  charging  of 
that  battery  at  the  normal  starting  rate.  Furthermore,  the  charg- 
ing resistance  connected  in  series  with  the  battery  further  reduces 
the  voltage  across  the  coil  of  the  circuit  breaker 'or  the  low  voltage 
relay  switch  (upon  reversal  of  battery  current),  thus  insuring  the 
tripping  of  the  breakers  or  the  low  voltage  relay  switch. 

Meter  Switch. — Each  charging  section  is  equipped  with  a 
special  2-pole  knife  switch  which  may  be  moved  to  a  position 
(without  opening  the  circuit)  so  that  the  battery  ammeter  and 
voltmeter  are  connected  to  the  charging  circuit,  thereby  indicat- 
ing the  charging  rate  in  amperes  and  the  voltage  of  the  battery 
at  once. 

Rheostats. — The  battery-charging  rheostats  usually  provide 
12  steps.  The  standard  rheostats  are  usually  designed  for  a 
particular  number  of  cells.  However,  each  rheostat  may  be  used 
for  charging  a  battery  composed  of  a  slightly  larger  number  of 


SMALL  D.C.  AND  A.C.  SWITCHBOARDS 


301 


cells,  requiring  the  same  charging  rate,  but  it  must  be  observed 
that  in  this  case  the  number  of  resistance  steps  available  for 
adjustment  will  be  reduced.  If  a  battery  is  to  be  boosted  at  a 
rate  higher  than  that  scheduled,  a  special  rheostat  will  be 
required. 

Lead  Batteries. — For  lead  batteries,  the  voltage  applied  across 
the  battery  terminals  will  be  increased  as  the  charge  progresses 


r  Charging! 
^ —-. 


FIG.   184. — Diagram    of    connections    with    magnetically    operated    switches. 

and  the  charging  current  will  be  maintained  approximately  con- 
stant, that  is,  at  the  given  starting  rate  until  near  the  end  of  the 
charging  period;  then  the  current  will  be  reduced  to  a  given 
finishing  rate,  and  will  be  maintained  approximately  constant 
throughout  the  remainder  of  the  charging  period. 

Edison  Battery. — For  nickel-iron  (Edison)  batteries  the  voltage 
applied  across  battery  terminals  will  be  increased  as  the  charge 


302 


SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


progresses  and  the  charging  current  will  be  maintained  approxi- 
mately constant  at  the  required  rate. 

Connections. — Fig.  184,  shows  the  diagram  of  connections 
with  magnetically  operated  switches. 

LIGHTING  AND  CHARGING  PANELS 

Light  and  Battery. — Where  a  switchboard  is  desired  for  con- 
trolling the  charging  of  batteries  used  in  lighting  service  and  on 
electric  vehicles,  but  only  one  battery  is  to  be  controlled  instead 
of  using  the  sectional  type  a  somewhat  simpler  construction  is 
employed  as  shown  in  Fig.  185. 


FIG.   185. — Light  &  battery  panels. 

One  class  of  panels  is  intended  for  use  in  residences  and  small 
isolated  plants  that  have  a  battery  to  supply  current  for  light- 
ing and  a  generator  for  charging  the  battery.  Only  single  panels 
are  made  and  the  capacity  of  the  generator  panels  is  limited  to 
75  amperes,  while  the  battery  panels  are  limited  to  a  normal  ca- 
pacity of  60  amperes.  On  single  section  panels  the  limit  is  100 


SMALL  D.C.  AND  A.C.  SWITCHBOARDS  303 

amperes  for  both  generator  and  battery  circuits.  The  circuit 
breakers  are  equipped  with  reverse  current  attachments  in  ad- 
dition to  the  plain  overload  trip  which  will  open  the  circuit  in 
case  the  charging  current  is  interrupted,  and  thus  prevent  the 
discharge  of  the  battery. 

When  battery-charging  apparatus  is  required  with  a  generator 
panel,  it  will  be  mounted  as  a  lower  section  of  the  panel,  except 
when  a  single  section  generator  and  battery-charging  panel 
is  specified. 

Conditions. — Three  conditions  are  provided  for  in  charging 
batteries  with  these  panels: 

First,  50-volt  generator  charging  30-volt  battery  connected 
directly  to  the  mains. 

Second,  125-volt  generator  charging  30-volt  battery.  The 
battery  is  charged  through  a  suitable  resistance. 

Third,  125-volt  generator  charging  125-volt  battery.  The 
battery,  in  this  case,  is  charged  with  two  sections  in  parallel, 
each  section  being  connected  through  a  suitable  charging  resist- 
ance. A  fixed  resistance  is  used  for  this  work,  the  variation  in 
voltage  being  taken  care  of  by  varying  the  field  of  the  generator. 

Constant  Potential  Charging. — This  method  of  charging  is  the 
constant  potential  charging  method;  that  is,  the  battery  is  thrown 
directly  on  the  circuit  and  allowed  to  become  charged.  When 
the  battery  and  charging  circuit  voltages  differ  sufficiently  to 
produce  a  charging  current  of  such  a  value  that  it  may  be  injurious 
to  the  battery,  a  charging  resistance  is  necessary.  The  value  of 
the  resistance  depends  on  the  number  of  cells  in  the  battery; 
type  of  cells  (or  voltage  at  beginning  of  charge  and  at  the  end  of 
charge) ;  charging  current  desired ;  and  the  line  or  generator  voltage. 
A  variable  resistance,  that  is  provided  with  faceplate  and  rotating 
arm,  mounted  apart  from  the  board,  can  be  used  to  obtain  the 
constant  current  method  of  charging.  However,  if  there  are 
but  one  generator  and  one  battery  circuit,  the  constant  current 
can  be  obtained  by  adjusting  the  generator  field  rheostat. 

Generator  Battery. — Where  a  panel  is  chosen  to  control 
a  lighting  circuit  in  addition  to  generator  and  battery  circuit, 
the  generator  voltage  must  be  maintained  for  the  lighting  circuit, 
and  consequently  a  charging  resistance  is  necessary,  either  of  the 
fixed  or  variable  type.  Electric  vehicle  charging  panels  are  made 
for  private  service,  where  one  battery  is  to  be  charged  and  the 
charging  current  is  taken  from  an  outside  source.  They  can, 


304         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


however,  be  used  when  the  current  is  furnished  by  a  motor-genera- 
tor set  or  engine  driven  generator,  by  adding  the  field  rheostat 
for  the  generator  to  the  panel  and  in  the  case  of  the  motor-genera- 
tor sets  by  mounting  one  of  the  lower  sections  on  the  same  frame. 
The  reverse-current  mechanism  furnished  with  the  carbon 
circuit  breaker  depends  for  its  action  on  the  sum  of  the  voltage 
and  current  coil  fields.  The  voltage  coil  field  is  the  stronger 

field  on  small  reversal  and  strong 
enough  at  zero  current  setting 
of  the  reverse-current  devices  to 
trip  the  breaker. 

Panels. — The  generator  panels 
are  a  modification  of  the  small 
generator  panels  described  later 
in  that  the  circuit  breaker  is 
equipped  with  reverse-current 
trip.  The  current  coil  in  the 
relay  is  designed  for  the  same 
carrying  capacity  as  the  circuit 
breaker  and  the  relay  is  cali- 
brated to  operate  with  a  battery 
which  has  the  same  capacity  as 
the  generator,  or  greater.  In 
case  the  battery  is  so  small  that 
it  requires  only  a  portion  of  the 
generator  capacity  to  completely  charge  it,  a  special  relay  or 
extra  switches  may  be  required.  Lower  sections  are  provided 
which  correspond  in  type  to  the  lower  sections  regularly  used 
with  the  generator  panels. 

The  lower  sections  are  for  use  with  30-volt  batteries,  and  with 
125-volt  batteries.  These  when  combined  with  the  generator 
panel  form  the  complete  panel  for  controlling  generator  and  bat- 
tery for  private  service. 

Fig.  186  shows  the  connections  of  a  single  section  battery 
panel  charging  the  battery  with  all  cells  in  series. 

COMBINATION  GENERATOR  AND  FEEDER  PANELS 

Where  the  panel  is  not  used  with  a  battery  the  reverse-current 
attachment  is  left  off  the  breaker  and  the  panels  are  designed  to 
provide  a  complete  switchboard  in  a  single  panel  of  one  or  two 
sections  to  control  one  generator  with  not  more  than  four  feeders. 


FIG.   186. — Connections  of  generator 
and  battery  panel. 


SMALL  D.C.  AND  A.C.  SWITCHBOARDS  305 

They  are  intended  for  small  isolated  plants  operating  direct- 
current  systems  of  250  volts  or  less. 

Limits. — The  capacity  of  a  panel  is  limited  to  400  amperes  for 
the  generator,  and  200  amperes  for  each  of  two  feeder  circuits, 
or  for  60  amperes  for  each  of  four  feeder  circuits.  Each  panel 
forms  a  complete  switchboard  and  is  not  designed  to  have  panels 
added  to  it. 

Panel  Size. — The  panel  consists  essentially  of  either  one  or  two 
sections  of  slate  1  inch  thick,  16  inches  wide,  with  ^-inch  bevel 
on  front  edges;  the  upper  section  being  24  or  36  inches  high,  and 
the  lower  section,  12,  18  or  24  inches  high.  The  upper  section 
contains  the  apparatus  for  the  control  of  the  generator  and  the 
lower  section  contains  that  for  the  control  of  the  various  feeder 
circuits. 

Frame. — The  frame  is  light  and  simple,  being  made  from  %- 
inch  gas  pipe  uprights  which  are  screwed  into  floor  flanges.  The 
total  height  of  the  frame  is  65  inches.  It  is  fitted  with  wall  brace 
ends  for  ^-inch  gas  pipe.  Pipe  and  foot  for  bracing  the  frame  to 
the  floor  or  wall  can  be  supplied  at  a  small  additional  price. 

Switches. — Single-throw  knife  switches  are  used  for  generator 
and  feeder  circuits.  When  it  is  desired  to  provide  for  a  separate 
source  of  power,  the  generator  panel  can  be  furnished  with  a 
double-throw  switch.  This  switch  will  be  mounted  horizontally 
instead  of  vertically. 

Protection. — Automatic  protection  is  provided  for  the  gene- 
rator circuit  by  a  single-pole  carbon  circuit  breaker,  or  by  en- 
closed fuses  mounted  on  the  front  of  the  panel.  Feeder  circuits 
are  protected  by  enclosed  fuses  mounted  on  the  front  of  the  panel. 

SMALL  PLANT  SWITCHBOARDS 

The  next  larger  size  of  D.C.  panels  using  slabs  48  inches  high 
on  pipe  framework  are  particularly  adapted  to  the  control  of 
from  one  to  three  generators  in  small  industrial  plants  and  cen- 
tral stations  operating  direct-current  2  wire  systems  of  250 
volts  or  less. 

Limits. — The  capacity  of  a  single  generator  panel  is  limited 
to  600  amperes,  and  that  of  a  complete  switchboard  composed 
of  these  panels  to  1500  amperes,  with  the  number  of  panels  limited 
to  six.  For  greater  capacities,  a  switchboard  composed  of  90- 
inch  high  panels  is  recommended. 


306         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


Panels. — Each  panel  consists  of  a  single  slate  slab  48  inches 
high  by  12,  16,  20  or  24  inches  wide,  1%  inches  thick,  with  96- 
inch  bevels  on  front  edges,  bolted  at  the  four  corners  to  the 
switchboard  frame.  This  frame  is  made  of  lK-inch  pipe  up- 
rights, resting  on  floor  flanges  and  supporting  the  necessary  panel 
and  top  iron  brackets,  to  which  the  panel  is  bolted.  The  total 
height  of  the  panel  is  76%  inches. 

Automatic  protection  is  provided  for  the  generator  circuits  by 
single-pole  carbon  circuit  breakers,  or  enclosed  fuse  blocks 
mounted  on  the  front  of  the  panel ;  for  feeder  circuits  by  single- 
pole  carbon  circuit  breakers,  enclosed  fuse  blocks  on  slate  bases 
mounted  on  brackets  on  rear  of  panel. 

MINING  SWITCHBOARDS 

Switchboards  of  this  type  are  suitable  for  substation  service  in 
mining  installations  controlling  motor-generator  sets  or  synch- 
ronous converters  typical  panel  arrangements  being  in  line  with 
Fig.  187  with  connections  as  shown  on  Fig.  188. 

Syn  DC  DC 

Motor  Panel  Gen  Panel  Gen  Panel. 


0 


ss 


Starter-   -L-J 


Remote  Mechanical  Control. 
FIG.  187. — Arrangement  of  M.G.  panels  for  mine  service. 

Scope. — These  mining  panels  are  particularly  adapted  for  the 
control  of  small  direct-current  generators  and  A.C.-D.C.  motor- 
generator  sets,  operating  2-wire,  grounded  negative,  direct- 
current  systems  of  600  volts  or  less;  and  for  the  control  of  small 
275-volt  converters  for  mine  service,  operating  2-wire,  grounded 
negative,  direct-current  systems. 

Engine  Generators. — Panels  for  the  control  of  275-volt,  direct 
current,  engine  driven  generators  are  in  general  similar  to  gene- 


SMALL  D.C.  AND  A.C.  SWITCHBOARDS 


307 


rator  panels  shown,  except  the  connections  on  the  rear  are  made 
for  a  grounded  negative  with  one  pole  of  the  2-pole  circuit 
breaker  being  connected  between  the  armature  and  the  series 
field  and  equalizer  connections,  and  the  other  between  positive 
and  bus.  As  the  negative  side  of  the  circuit  is  grounded,  no 


FIG.  188.— Diagram  of  connections  for  M.G.  sets  for  mine  service. 

ground  detector  outfit  is  supplied.  The  voltmeter  switch  is  two 
point,  the  negative  side  of  the  voltmeter  being  connected  to 
ground. 

Panels  for  the  control  of  600-volt,  engine  driven  generators  are 
similar  to  the  275-volt  panels  described  above,  except  that  600- 
volt  apparatus  is  supplied. 

Motor  Generators. — Panels  for  the  control  of  direct-current 
generators  which  are  part  of  motor-generator  sets,  with  over- 


308         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

load  protection  in  the  motor  circuit,  will  have  the  connections 
modified  in  that  the  single-pole  carbon  circuit  breaker  will  be 
inserted  in  the  positive  side  of  the  circuit.  The  carbon  breaker 
will  also  be  equipped  with  a  low  voltage  release  for  tripping  it 
when  the  motor  breaker  opens. 

Feeders. — Panels  for  the  control  of  feeders  are  similar  to  light 
and  power  feeder  panels,  except  that  a  single-pole  knife  switch 
is  furnished  in  place  of  each  2-pole  switch,  and  the  switches 
are  for  600  volts  for  the  600-volt  panels. 

Motors. — Panels  for  the  control  of  induction  motors  are 
furnished  in  the  form  of  sub-panels  to  be  mounted  directly  below 
the  direct-current  generator  panel,  on  the  pipe  frame  legs. 

Panels  for  the  control  of  self-starting  synchronous  motors  are 
furnished  as  separate  switchboard  panels  to  stand  adjacent  to 
the  direct-current  generator  panel. 

Starters. — The  A.C.  motor  starter  is  a  double-throw  oil  circuit 
breaker,  non-automatic  for  starting,  and  automatic  with  over- 
load inverse  time  limit  and  low  voltage  release  for  running.  The 
handles  are  mechanically  interlocked  so  that  the  starting  side  of 
the  breaker  must  be  closed  first  and  that  the  running  side  can 
only  be  closed  within  a  fixed  time  interval  after  starting  side  had 
been  opened. 

The  starting  position  magnetizes  the  auto  transformers  and 
connects  the  motor  to  the  starting  voltage,  the  tap  leads  of  the 
transformer  being  permanently  connected  to  the  motor  leads. 
In  passing  to  the  running  position  the  auto  transformers  are 
disconnected  from  the  line  and  full-line  voltage  is  applied  to  the 
motor. 

The  starter  for  3-phase  service  is  4-pole  double  throw  with 
special  moving  contact  arrangement. 

Starting  Combinations.-^-As  an  alternative,  a  combination  of 
remote  mechanically  operated  automatic  3-pole  and  non-auto- 
matic 4-pole  type  breakers  can  be  had.  The  3-pole  breaker 
constitutes  the  running  breaker.  It  is  overload  automatic,  with 
inverse  time  limit  and  low  voltage  release  mechanisms.  The  4- 
pole  breaker  is  the  starting  breaker;  it  magnetizes  the  auto  trans- 
formers and  connects  the  motor  to  the  starting  voltage  from 
separate  handles  mechanically  interlocked  so  that  one  breaker 
only  can  be  closed  at  one  time.  A  two  handle  cover  plate  will  be 
supplied  and  current  transformers  for  use  with  the  automatic 
breaker. 


SMALL  D.C.  AND  A.C.  SWITCHBOARDS  309 

This  combination  is  made  for  remote  mechanical  operation 
only  and  is  applicable  only  for  starting  with  two  single-phase 
auto  transformers. 

The  switching  equipment  for  motors  of  capacities  exceeding  the 
ratings  of  the  double-throw  breaker  are  made  up  of  either  two  or 
three  single-throw  breakers  as  follows: 

Motors  started  by  means  of  two  single-phase  auto  transformers 
have  a  standard  3-pole  running  breaker  and  a  special  4-pole  start- 
ing breaker;  motors  started  by  means  of  a  3-phase  auto  trans- 
former have  a  standard  3-pole  running  breaker  and  two  special 
3-pole  starting  breakers  operating  in  tandem. 

Time  Element. — The  inverse  time  element  feature  is  provided 
in  connection  with  the  overload  trip  on  the  circuit  breaker  or  au- 
to starter,  so  that  the  motor  circuit  will  not  be  opened  on  moment- 
ary overloads,  such  as  obtain  when  the  switches  are  moved  from 
the  starting  to  the  running  position.  The  time  in  which  the  over- 
load trip  will  operate  is  inversely  proportional  to  the  amount  of 
overload,  tripping  being  instantaneous  in  case  of  a  short  circuit. 

The  overload  tripping  range  is  usually  from  80  to  160  per  cent, 
of  the  current  rating  of  the  current  transformers  included  with 
the  panel  equipment. 

Low  Voltage. — All  circuit-breaker  equipments  have  a  low 
voltage  trip  which  opens  the  running  breaker  when  the  voltage 
has  dropped  to  approximately  one-half  its  normal  value.  This 
feature  is  included  to  guard  against  an  excessive  current  due  to 
the  return  of  power  to  a  motor  which  may  be  out  of  phase  or  at 
rest.  For  voltages  up  to  and  including  550,  the  low  voltage  coil 
with  series  resistance  is  connected  directly  to  the  line.  For  higher 
voltages,  a  voltage  transformer  with  primary  fuse  blocks  and 
fuses  is  included. 

Auxiliary  Switch. — The  handle  of  the  running  circuit  breaker 
is  equipped  with  an  auxiliary  switch  which  serves  to  operate  the 
low  voltage  trip  circuit  of  the  direct-current  generator  breaker  of 
the  motor-generator  set,  when  the  alternating-current  breaker 
opens. 

Reversal. — If  the  direct-current  generator  of  a  motor-generator 
set  operates  in  parallel  with  an  independent  source  of  direct- 
current  power,  the  set  will  run  inverted  upon  the  interruption  of 
the  alternating-current  power  and  hold  up  the  alternating-current 
voltage.  The  independent  source  of  direct-current  powermay  be 
a  motor-generator  set  (or  a  synchronous  converter)  supplied 


310         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

from  a  separate  alternating-current  source,  a  generator  driven 
by  a  prime  mover,  or  a  battery.  In  order  to  prevent  motoring 
from  the  direct-current  bus  bars,  and  to  disconnect  the  set,  a 
reverse-current  relay  should  be  included  with  the  direct-current 
generator  panel  equipment  and  so  connected  as  to  trip  the  alter- 
nating-current breaker  upon  current  reversal.  With  the 
electrical  interlock  mentioned  in  the  preceding  paragraph  the 
direct-current  breaker  is  tripped  on  the  opening  of  the  alter- 
nating-current breaker  and  the  set  is  thus  completely  discon- 
nected in  case  of  alternating-current  power  interruption. 

Rupturing  Capacity. — The  short-circuit  amperes  which  the 
breaker  may  be  called  upon  to  interrupt  must  be  considered  in 
every  case  before  applying  the  standard  equipments.  If  the  total 
capacity  of  generating  and  synchronous  apparatus  connected  close 
to  the  motor  is  sufficient  to  deliver,  under  short  circuit,  a  current 
in  excess  of  the  rupturing  capacity  of  the  running  breaker  in- 
cluded in  the  standard  equipment,  special  consideration  is  neces- 
sary. It  may  be  possible  in  this  case  to  modify  the  standard 
equipment  by  replacing  the  dashpot  inverse  time  limit  attach- 
ment by  direct  trip  attachment,  and  relay  equipment  giving  a 
definite  minimum  time  delay,  and  thus  avoid  the  necessity  of  a 
heavier  duty  breaker.  Where  the  interrupting  capacity  required 
is  more  than  twice  the  rating  of  the  breaker  in  the  standard  equip- 
ment, it  is  necessary  either  to  replace  the  running  breaker  by  one 
of  suitable  interrupting  capacity  or  supply  a  breaker  of  suitable 
interrupting  capacity  in  series,  which  is  set  to  open  ahead  of  the 
running  breaker  of  the  standard  equipment  in  case  of  a  short 
circuit.  The  breaker  at  the  power  house  may  often  serve  this 
purpose  where  the  motor  is  supplied  from  a  transmission  line. 
In  the  latter  case  the  breaker  of  the  standard  equipment  must  be 
given  a  definite  minimum  time  delay  as  mentioned  above.  It 
may  be  necessary  also  to  use  heavier  duty  starting  breakers  on 
a  heavy  capacity  system. 

Auto  Reclosing  Breakers. — These  circuit  breakers  can  be 
applied  where  it  is  desired  to  insure  that  circuits  will  not  unneces- 
sarily remain  open  when  overload  conditions  have  been  removed. 
Power  is  automatically  put  back  on  the  circuit,  as  soon  as  con- 
ditions permit,  and  the  expensive  delays  due  to  failure  of  power 
is  reduced  to  a  minimum. 

Automatic  reclosing  circuit  breakers  can  be  furnished  in  place 
of  the  plain,  automatic,  carbon  breakers.  The  automatic  re- 


SMALL  D.C.  AND  A.C.  SWITCHBOARDS  311 

closing  circuit  breaker  is  essentially  a  solenoid  operated  breaker, 
the  main  contacts  being  held  closed  by  the  action  of  a  solenoid. 
When  an  overload  or  short  circuit  occurs  on  the  load  side  of  the 
line  the  solenoid  circuit  is  caused  to  open.  This  remains  open  for 
a  definite  time,  resulting  in  an  immediate  opening  of  the  carbon 
breaker  (owing  to  a  dashpot  element),  and  then  automatically 
closes  only  when  the  overload  or  short  circuit  has  disappeared. 
Auxiliary  devices  are  usually  necessary. 

When  two  or  more  generators  operate  in  parallel  and  each 
generator  circuit  is  provided  with  an  automatic  reclosing 
breaker,  a  special  master  relay  is  required  so  that  all  generator 
breakers  will  be  opened  or  closed  simultaneously. 

When  the  feeder  circuits  are  not  independent,  but  tie  in  with 
feeder  circuits  from  other  stations,  a  feeder  relay  is  required  with 
each  tie-in  feeder  circuit  to  control  the  reclosing  of  the  automatic 
reclosing  breaker  with  reference  to  the  load  conditions,  whether 
the  line  is  energized  from  the  remote  source  of  power  or  not,  at 
the  particular  time  the  breaker  opens.  This  applies  also  to  the 
automatic  reclosing  breaker  of  the  generator  circuit  if  there  is 
only  one  connected  to  the  bus  from  which  several  tie-in  feeder 
circuits  are  fed,  or  to  the  master  relay  if  there  are  several  genera- 
tors operating  in  parallel  on  a  tied-in  system. 

When  there  is  the  possibility  of  a  reversal,  the  generator 
breakers  should  also  be  equipped  with  a  special  reverse  current 
relay  which  slips  over  the  studs  of  the  breaker. 

Synchronous  Motor  Panels. — These  usually  have  no  field 
switches.  A  self-starting  synchronous  motor  is  usually  started 
with  the  field  circuit  closed  through  the  armature  of  its  individual 
exciter  if  connected  to  the  motor  shaft;  or  if  no  exciter  is  provided 
and  the  motor  is  excited  from  the  direct-current  generator  which 
it  drives,  the  motor  field  is  closed  through  the  generator  armature. 
The  motor  field  is  thus  short-circuited  at  stand-still  and  is  gradu- 
ally excited  as  the  motor  comes  up  to  speed. 

A  2-pole  double-throw  field  switch  must  be  supplied  when 
the  motor  field  is  excited  from  a  separate  source  of  power,  or 
from  an  exciter  not  connected  to  the  motor  shaft.  The  left-hand 
switch  studs  are  connected  together  by  a  copper  strap.  The 
field  switch  is  in  the  left-hand  position  until  the  motor  has  come 
up  to  synchronous  speed.  It  is  thrown  to  the  right-hand  or 
normal  position  before  the  motor  is  connected  to  full  line  voltage. 


312         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

The  rheostat  is  in  series  with  the  field  in  the  starting  position  as 
well  as  in  the  normal  position  of  the  field  switch. 

Motor-generator  Sets. — When  these  are  used  for  275-volt 
direct-current  service  they  have  the  motor  field  excited  across  the 
direct-current  generator  terminals.  Motor-generator  sets  for  550 
volt  direct-current  service  may  have  a  separate  125-volt  exciter 
connected  to  the  same  shaft,  or  the  motor  field  may  be  excited 
from  an  exciter  independent  of  the  motor-generator  set. 


FIG.   189. — Diagram  of  connections  for  synchronous  converters  for  mine  service. 


For  synchronous  converter  service  in  mines,  combination  A.C.- 
D.C.  panels  can  be  supplied  containing  carbon  breaker,  ammeter, 
voltmeter  and  knife  switch  for  the  D.C.  circuit,  reactive  factor 
meter  and  oil  breaker  for  A.C.  with  a  separate  panel  for  starting 
with  connections  as  per  Fig.  189. 

Combination  Panels. — For  isolated  plant  service  combination 
panels  can  be  provided  to  control  one  D.C.  generator  and  any 


SMALL  D.C.  AND  A.C.  SWITCHBOARDS 


313 


number  of  D.C.  feeders  up  to  four.  These  panels  are  intended 
for  use  in  isolated  plants  operating  a  single  D.C.  generator  of  250 
volts  or  less  and  not  over  600-amperes  capacity. 

Each  panel  consists  of  a  single  slate  slab,  48  inches  high  by  20 
inches  or  24  inches  wide,  by  1>^  inches  thick,  with  %-inch  bevels 
on  front  edges,  bolted  at  the  four  corners  to  the  frame.  The 
total  height  is  76%  inches. 

Automatic  protection  is  provided  for  the  generator  circuit  by  a 
single-pole  carbon  circuit  breaker,  or  by  enclosed  fuses  mounted 
on  the  front  of  the  panel;  for  the  feeder  circuits,  by  enclosed  fuses 
mounted  on  the  front  of  the  panel. 

The  main  connections  on  the  back  of  the  panels  are  of  bare 
copper  strap  and  are  cut,  bent,  and  assembled  before  shipment. 


FIG.  190. — Connections  of  three-wire 
generators  with  four-pole  breaker. 


FIG.  191. — Connections  of  three-wire 
generators  with  two-pole  breaker. 


Three- Wire  Panels.— These  48-inch  high  panels  are  also  suit- 
able for  use  with  3-wire  D.C.  generators  connected  to  utilize 
4-pole  circuit-breaker  protection  as  shown  in  Fig.  190,  or 
2-pole  circuit- breaker  protection  as  shown  in  Fig.  191. 

These  3-wire  switchboards  are  designed  for  the  control  of 
from  one  to  three  generators  in  lighting  and  power  plants  of 
moderate  capacity  operating  direct-current  3-wire  systems. 

The  capacity  of  a  single  generator  panel  is  limited  to  600  am- 
peres, and  that  of  a  complete  switchboard  composed  of  three 
panels  to  1500  amperes.  For  greater  capacities  a  switchboard 
composed  of  90-inch  high  panels  is  recommended. 


314          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Each  panel  consists  of  a  single  slate  slab  48  inches  high,  1% 
inches  thick,  with  %-inch  bevels  on  front  edges,  bolted  at  the 
four  corners  to  the  frame.  The  frame  is  made  of  1^-inch  pipe 
uprights,  resting  in  tapped  floor  flanges  with  the  necessary  panel 
and  top  iron  brackets.  The  total  height  is  76%  inches. 

Meters. — Polarized  ammeters  and  voltmeters  are  regu- 
larly furnished  with  these  panels.  With  the  ammeters  there  are 
supplied  ammeter  shunts  for  mounting  on  the  generator  frame, 
and  shunt  leads  40  feet  long. 

Switches. — Knife  switches,  either  single  or  double  throw,  are 
used  on  generator  and  feeder  panels.  Switches  are  not  provided 
for  disconnecting  the  balance  coils  from  the  collector  rings  on  the 
generator,  as  these  circuits  can  be  opened  by  lifting  the  collector 
brushes.  If  switches  are  desired  in  these  circuits,  double-pole 
single-throw  knife  switches  can  be  provided  and  mounted  on  the 
panel,  or  on  a  sub-panel.  The  omission  of  these  switches  from 
the  balance  coil  circuits  effects  a  saving,  as  it  eliminates  the 
necessity  of  running  cables  from  the  collector  brushes  and  balance 
coils  to  the  switchboard. 

Protection. — Automatic  protection  for  the  generator  circuit  is 
provided  by  a  4-pole  carbon  circuit  breaker  automatically  trip- 
ped through  relays  actuated  by  the  full  armature  current,  or  by 
a  2-pole  double  coil  overload  carbon  breaker. 

Automatic  protection  for  feeder  circuits  is  provided  by  2- 
pole  circuit  breakers,  three  single-pole  circuit  breakers  actuated 
by  a  common  trip,  or  enclosed  fuses. 

Where  generators  are  operating  in  parallel,  positive  and  nega- 
tive equalizer  bus  bars  are  necessary  in  addition  to  the  main  bus 
bars.  These  extend  behind  the  generator  panels  but  are  not 
continued  back  of  the  feeder  panels. 

Code  Rule. — With  3-wire  direct-current  generators,  the 
National  Electrical  Code  requires  that  the  "safety  device  consist 
of  either  a  double-pole  double  coil  overload  circuit  breaker,  or  a 
4-pole  circuit  breaker  connected  in  the  main  and  equalizer 
leads,  and  tripped  by  means  of  two  overload  devices,  one  in  each 
armature  lead."  In  short,  the  National  Electrical  Code  re- 
quires that  the  safety  device  be  actuated  by  the  full  armature 
current. 

Comparison. — A  Comparison  between  the  two  methods  shows 
the  following: 


SMALL  D.C.  AND  A.C.  SWITCHBOARDS  315 

Two-pole  breaker  protection  requires: 
2-pole  carbon  breaker. 

Six  leads  between  generator  and  switchboard.     (See  diagram  of  con- 
nections.) 

Cable  duct  and  installation  of  same  for  six  main  generator  leads. 
Ammeter  shunts  mounted  on  switchboard. 
Two  sets  of  short  ammeter  shunt  leads. 
Four-pole  breaker  protection  requires: 

4-pole  carbon  breaker  with  low  voltage  release  device  for  tripping  by 

relays. 

Two  overload  relays. 

Four  leads  between  generator  and  switchboard.     (See  diagram  of  con- 
nections.) 

Cable  duct  and  installation  of  same  for  four  main  generator  leads. 
Ammeter  shunts  mounted  on  generator  frame. 

Four  sets  of  ammeter  shunt  leads  of  a  length  at  least  sufficient  to  reach 
from  ammeter  shunt  on  generator  frame  to  meters  and  relay  on  board, 
through  main  lead  or  separate  ducts. 

Costs. — From  the  above  comparison,  it  can  be  seen  that  the 
cost  of  the  switchboard  panel  equipment  is  greater  with  the 
4-pole  breaker  protection  than  with  the  2-pole  breaker  protection. 
However,  the  added  cable  and  cable  duct  cost,  including  also  the 
added  expense  of  installation,  may  be  found  to  make  the  cost  of 
the  total  equipment  greater  with  the  latter  method  of  protection 
than  with  the  former.  This  becomes  true  as  the  distance  be- 
tween the  generator  and  the  switchboard  increases,  and  as  the 
size  of  the  cables  and  ducts  increases. 

The  following  table  gives  the  distance  between  generator  and 
switchboard  beyond  which  it  will  be  found  in  general  that  the  total 
equipment  cost  of  2-pole  breaker  protection  will  be  greater  than 
total  equipment  cost  of  4-pole  breaker  protection. 

200  kw.  250-volt  generator  18  feet 

150  kw.  250-volt  generator  22  feet 

100  k\v.  250-volt  generator  28  feet 

75  kw.  250-volt  generator  33  feet 

60  kw.  250-volt  generator  38  feet 

50  kw.  250-volt  generator  40  feet 

25  kw.  250-volt  generator  50  feet 

WELDING  PANELS 

For  welding  service  48-inch  panels  can  be  utilized  to  ad- 
vantage. Welding  by  means  of  the  electric  arc  is  accomplished 
by  drawing  an  arc  between  a  metal  or  carbon  electrode  of  an 
electric  circuit,  and  the  metals  to  be  welded.  The  electrode 


316         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


is  usually  the  negative  terminal  of  the  circuit,  whereas  the  metal 
to  be  welded  is  the  positive  terminal.  Direct  current  is  commonly 
used  for  arc  welding,  as  it  requires  less  current  than  alternating 
for  the  same  welding  effect  and  also  gives  the  better  results. 

Processes. — Arc  welding  is  divided  into  two  commercial  proc- 
esses: Carbon,  or  Graphite,  Electrode  Process,  in  which  the 
arc  is  drawn  between  metal  to  be  welded  and  a  carbon,  or  gra- 
phite, electrode;  and  the  Metal  Electrode  Process,  in  which  the 

arc  is  drawn  between  metal 
to  be  welded  and  a  metal 
electrode. 

The  current  for  arc  welding 
may  be  obtained  from  any 
convenient  direct-current 
source,  although  it  is  com- 
monly taken  from  a  motor- 
generator  set.  Several  weld- 
ing circuits  can  be  connected 
to  one  generator  circuit,  the 
number  depending  on  the 
capacity  of  the  generating 
equipment  and  on  the  num- 
ber of  operators  working  at 
any  one  time. 

Where  only  one  welding  circuit  is  connected  to  the  generator, 
both  the  generator  circuit  and  the  welding  circuit  may  be  con- 
trolled from  a  single  switchboard  panel,  which  is  known  as  a 
combination  control  panel  connected  as  per  Fig.  192,  or  an  in- 
dividual generator  panel  may  be  used  to  control  the  generator 
and  a  separate  outlet  panel  to  control  the  welding  circuit.  Where 
several  welding  circuits  are  connected  to  one  generator  circuit, 
the  generator  may  be  controlled  either  from  a  separate  generator 
panel  or  from  a  combination  control  panel;  in  the  latter  case  one 
of  the  welding  circuits  is  connected  to  the  combination  panel  and 
the  remainder  to  outlet  panels,  while  in  the  former  case  an  outlet 
panel  must  be  provided  for  each  welding  circuit. 

Capacities. — The  combination  generator  and  welding  panels 
range  in  capacities  from  150  amperes  to  1000  amperes  for  the 
generator  equipment  and  up  to  750  amperes  for  the  welding  equip- 
ment. On  the  1000-ampere  combination  panel  the  control  for 
the  welding  circuit  is  of  750-amperes  capacity;  on  all  other  combi- 


loSh.Fld. 

Conc.for  use  witb  Carbon 

Electrode  or  when  Reactor 

la  not  furnished. 


furnished  fcr  use  tcltb 
Metal  Electrode  only. 


:  Electrode 

FIG.  192. — Diagram  of  connections  for 
welding  panels. 


SMALL  D.C.  AND  A.C.  SWITCHBOARDS 


317 


nation  panels  the  control  for  the  welding  circuit  is  of  the  same 
capacity  as  the  generator  circuit.  The  separate  generator  panels 
are  for  capacities  ranging  from  150  to  1000  amperes;  the  outlet 
panels  are  for  capacities  of  200,  350  and  600  amperes. 

Each  panel  consists  of  a  single  section,  48  inches  high  by  16, 
20  or  24  inches  wide,  and  1^  inches  thick,  with  %-inch  bevels 
on  front  edges,  except  the  metal  electrode  outlet  panel,  which  is 
36  inches  high.  The  panels  are  mounted  on  l^-inch  pipe  frames, 
complete  with  floor  brace,  the  total  height  of  which  is  76^  inches. 

Single-pole  carbon  circuit  breakers  provide  automatic  overload 
protection  for  both  the  generator  and  welding  circuits. 


p'.o  o  o 
o  o 


LOW  VOLTAGE  A.C.  SWITCHBOARDS 

For  moderate  capacity  low  voltage  A.C.  circuit  switchboards 
are  particularly  designed  for  the  control  of  from  one  to  three  gen- 
erators in  small  industrial  plants  and 
central  stations  operating  alternating- 
current  systems  below  500  volts.  Fig. 
193  shows  a  typical  440-volt  switch 
board. 

Limits. — The  capacity  of  a  single 
generator  panel  is  limited  to  600 
amperes,  and  that  of  a  complete  switch- 
board composed  of  these  panels,  to  1500 
amperes,  with  the  number  of  panels 
limited  to  five.  For  greater  capacities, 
a  switchboard  composed  of  90-inch  high 
panels  is  recommended. 

Panels. — Each  panel  consists  of  a 
single  slate  slab  48  inches  high  by  16  or 
20  inches  wide,  1%  inches  thick,  with 
%-inch  bevels  on  front  edges  mounted 
on  a  lK-inch  pipe  frame.  The  total 
height  of  the  panel  is  76%  inches. 

Protection. — No    Overload     protection          FIG.  193.— Arrangement 

is  provided  for  the  main  or  field  circuits    hL^twitc'hboard  We^S' 
of  alternating-current  generators.     The 

panels  for   feeder  circuits  include  enclosed   fuses  mounted  on 
the  rear  of  the  panel. 

Meters. — On  generator  panels,  one  ammeter  is  furnished  for 


318         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


each  phase.     On  feeder  panels,  one  ammeter  is  furnished  for  each 

2,  or  3-phase  circuit. 

The  generator  panels  are  designed  to  have  the  exciter  rheostat 

supported  on  a  tetrapod  mounted  on  the  rear  of  the  panel,  with 
the  generator  rheostat  separately 
mounted  and  operated  by  a  sprocket- 
and-chain  transmission. 

Synchronizing. — These  panels  are 
designed  for  synchronizing  between  the 
incoming  machines  and  the  bus  bars. 
A  six-point  synchronizing  switch  and 
an  incandescent  lamp  are  furnished 
with  each  generator  panel  and  one 
synchronizing  key  is  supplied  with  each 
switchboard,  with  connections  as  per 
Fig.  194.  A  synchronoscope  with  the 
necessary  voltage  transformers  can  be 
supplied,  if  desired. 

Each  generator  panel  is  designed  to 
have  the  generator  field  connected 
through  a  2-pole  switch  with  field 

discharge   contacts  to  a  single  exciter.     If  parallel  operation  of 

exciters  is  desired,  exciter  panels  are  needed. 


FIG.  194. — Diagram  of 
connections  440  volt  A.C. 
switchboard. 


HIGH  VOLTAGE  A.C.  SWITCHBOARDS 

Similar  panels  are  available  for  1200-2400  volts  and  up  to  200- 
amperes  capacity.  These  switchboards  are  particularly  adapted 
to  the  control. of  single  or  parallel  operated  alternators  in  small 
industrial  plants  and  central  stations,  see  Fig.  195. 

Limits. — The  capacity  of  a  single  generator  or  feeder  panel  is 
limited  to  200  amperes  and  that  of  a  complete  switchboard  to 
400  amperes.  For  greater  capacities,  a  switchboard  with  90-inch 
panels  is  recommended. 

Panels. — Each  panel  consists  of  a  single  slab,  48  inches  high  by 
13^  inches  thick,  with  %-inch  bevels  on  front  edges,  bolted  at 
the  four  corners  to  a  1^-inch  pipe  frame.  The  total  height  of  the 
panels  is  76%  inches. 

Protection. — Standard  panels  provide  no  automatic  protection 
for  the  main  or  field  circuits  of  alternating-current  generators. 

When  a  single  generator  panel  controlling  one  feeder  is  installed, 


SMALL  D.C.  AND  A.C.  SWITCHBOARDS 


319 


automatic  protection  for  the  feeder  side  of  the  non-automatic 
oil  circuit  breaker  may  be  obtained  by  providing  a  subsection 
with  fuses,  to  be  mounted  immediately  below  the  generator 
panel  on  the  frame.  An  automatic  oil  circuit  breaker  can 
be  substituted  for  the  non-automatic  circuit  breaker  and  fuse 
section.  The  advantages  of  the  automatic  circuit  breaker  are 
that  it  is  quickly  and  easily  closed  after  opening  the  circuit, 


Fia.   195. — Arrangement  of  small  2400-volt  Westinghouse  switchboard. 


cannot  be  held  in  a  closed  position  while  an  overload  condition 
exists  on  the  line,  and  eliminates  the  trouble  and  expense  of  re- 
placing the  fuses. 

The  generator  panels  are  designed  to  have  the  exciter  rheostat 
supported  on  a  bracket  mounted  on  the  rear  of  the  panel,  with  the 
generator  rheostat  separately  mounted  and  operated  by  a 
sprocket-and-chain  transmission. 

Each  generator  panel  is  designed  to  have  the  generator  field 
connected  through  a  2-pole  field  switch  with  field  discharge 


320         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

contact,  to  a  single  exciter.  If  parallel  operation  of  exciters  is 
desired,  exciter  panels  should  be  ordered. 

Ground  Detector. — A  voltage  transformer  having  a  lamp  across 
its  secondary  and  arranged  for  connecting  to  each  bus  wire  is 
supplied  for  indicating  grounds. 

Synchronizing. — A  synchronizing  receptacle  and  an  incandes- 
cent lamp  for  synchronizing  between  machines  are  furnished 
with  each  generator  panel.  The  same  transformer  used  in 
connection  with  the  voltmeter  is  used  for  synchronizing.  If 
synchronizing  between  bus  and  machine  is  desired,  one  voltage 
transformer  with  fuses  for  connecting  to  bus  is  needed.  A  syn- 
chronoscope  can  be  supplied  if  desired. 

Feeder  panels  are  supplied  with  overload  automatic  oil  cir- 
cuit breakers  or  non-automatic  oil  circuit  breakers  with  rear 
connected  fuses.  These  fuses  are  removable  from  the  front  of 
the  panel,  but  have  no  live  parts  exposed. 


CHAPTER  XIII 

LARGE  HAND  AND  ELECTRICALLY  OPERATED  PANEL 

SWITCHBOARDS  FOR  D.C.  GENERATORS  AND 

SYNCHRONOUS  CONVERTERS 

Standards. — For  the  control  of  D.C.  generators,  the  D.C.  end 
of  synchronous  converters  and  D.C.  feeders  for  250  volts,  2-wire 
and  3-wire  light  and  power  service  and  600-volt  railway  service, 
panels  with  a  total  height  of  90  inches  have  been  standardized 
by  various  switchboard  builders.  The  original  Westinghouse 
panel  divisions  for  this  class  of  switchboard  were  65  and  25  inches, 


•    FIG.  196. — Westinghouse  railway  switchboard. 

and  corresponding  G.  E.  divisions  being  62  and  28  inches.  The 
present  three  section  panels  of  these  companies  are  25  inches,  45 
inches  and  20  inches,  and  31  inches,  31  inches  and  28  inches  res- 
pectively. Other  switchboard  builders  have  used  these  or  other 
panel  divisions  with  the  same  total  height. 

Westinghouse  Railway  Switchboard. — Fig.  196  shows  a  typical 
Westinghouse    switchboard    installed    in    a    large    synchronous 
21  321 


322        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

converter  substation.  Like  most  switchboards  for  railway  serv- 
ice, there  is  only  one  D.C.  polarity,  the  positive,  brought  to  the 
board,  the  negative  and  equalizer  busses  running  between  the 
machines  and  not  being  located  on  the  switchboard  panel. 

The  ten  panels  near  the  right-hand  end  of  the  switchboard  are 
feeder  panels  having  single-pole  carbon  break  circuit  breakers 
connected  to  the  main  600-volt  bus  at  their  upper  stud,  the  lower 
stud  being  connected  to  the  top  stud  of  the  knife  switch,  and  the 
ammeter  shunt  being  located  in  the  strap  connections  between  the 
breaker  and  switch.  The  next  six  feeder  panels  are  provided  with 
double-throw  knife  switches  instead  of  single-throw,  the  lower 
throw  of  these  knife  switches  connecting  to  a  transfer  bus,  this 
transfer  bus  in  turn  being  connected  to  the  main  bus  through  a 
circuit  breaker  and  switch.  With  this  arrangement  any  of  these 
six  feeder  circuits  can  be  operated  either  through  its  own  circuit 
breaker  or  through  the  circuit  breaker  on  the  transfer  panel. 

Beyond  the  feeder  panels  are  D.C.  load  panels,  panels  for  the 
D.C.  end  of  the  converter,  panels  for  the  transformers  feeding  the 
converter,  and  panels  for  the  incoming  A.C.  line  circuit. 

On  this  particular  switchboard  where  the  panel  sections  are 
20  inches,  45  inches  and  25  inches,  the  upper  sections  of  the  D.C. 
panels  are  reserved  for  the  carbon  circuit  breakers,  the  middle 
for  the  instruments  and  switches  and  the  bottom  sections  of  the 
feeder  panels  are  left  blank.  On  the  D.C.  converter  panels  the  bot- 
tom sections  contain  watthour  meters,  while  on  the  A.C.  panels 
these  contain  relays. 

G.  E.  Power  Switchboard. — Fig.  197  shows  a  typical  Gene- 
ral Electric  double  polarity  2- wire  power  station  switchboard 
controlling  four  generators  and  eight  feeder  circuits.  With  the 
arrangement  shown,  the  positive,  negative  and  equalizer  leads  of 
each  generator  are  brought  to  the  switchboard.  The  two 
generator  panels  at  right-hand  end  of  switchboard  each  have  a 
three-pole  switch,  while  the  two  at  the  left-hand  end  have  each 
three  single-pole  switches.  The  carbon  breaker  is  in  the  positive 
circuit  of  each  generator.  Each  of  the  feeder  circuits  is  provided 
with  a  carbon  breaker  in  the  positive  circuit  and  a  knife  switch  in 
the  negative  circuit. 

With  these  three-section  panels  divided  into  sections  31  inches, 
31  inches  and  28  inches,  the  upper  31  inch  sections  are  reserved 
for  circuit  breaker  and  meter,  while  the  middle  section  contains 
the  knife  switches  on  the  feeder  circuits,  and  on  the  generator 


LARGE  PANEL  SWITCHBOARDS 


323 


FIG.  197. — General  Electric  Co.  three  section  switchboard. 


FIG.  198. — Pittsburgh  Electric  Co.  switchboard,  front  view. 


324        SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

circuits  the  field  rheostat  and  voltmeter  receptacle  in  addition  to 
the  knife  switches.  Two  D.C.  voltmeters,  located  on  a  swinging 
bracket,  are  placed  at  the  end  of  the  board. 

Pittsburgh  Electrical  Power  Board. — Fig.  198  shows  a  some  what 
similar  D.C.  switchboard  built  by  the  Pittsburgh  Electric  and  Ma- 
chine Works,  utilizing  Cutter  (I.T.E.)  circuit  breakers,  Weston 
indicating  meters,  Sangamo  watthour  meters  and  knife  switches 


FIG.   199. 

of  their  own  design.  This  is  a  double  polarity  switchboard  con- 
trolling two  750-K.W.  Synchronous  converters  and  a  smaller 
unit  as  well  as  five  outgoing  feeder  circuits. 

Fig.  199  shows  the  rear  view  of  this  same  switchboard  illus- 
trating the  angle  frame  iron  construction  and  the  simplicity  of 
the  bus  bar  arrangement  due  to  the  use  of  laminated  stud  circuit 
breakers  and  switches. 

This  switchboard  has  its  panels  in  three  sections,  20  inches,  50 
inches  and  20  inches  high,  the  top  slab  being  reserved  for  the 
carbon  circuit  breaker,  the  middle  slab  for  the  instruments  and 
switches,  and  the  lower  slab  being  left  blank. 


LARGE  PANEL  SWITCHBOARDS 


325 


Cutter  3 -wire  Breakers. — For  use  with  3-wire  D.C.  gener- 
ators that  are  provided  with  series  fields  in  the  positive  and 
negative  circuits,  a  special  arrangement  of  4-pole  carbon  breaker 
is  furnished  by  the  Cutter  Company  as  shown  in  Fig.  200. 

With  this  arrangement  the  main  positive  and  main  negative 
circuits  are  run  from  the  armature  of  the  generator  to  the  circuit- 
breaker  stud  passing  through  the  overload  coil  with  a  reversal 
feature  in  one  circuit,  thence  to  the  lower  outside  main  stud,  the 


FIG.  200. — Cutter  circuit  breaker  for  three-wire  generator. 

leads  being  then  brought  back  to  the  generator  in  order  to  pass 
through  the  series  fields  in  the  positive  and  in  the  negative  circuits. 
The  two  outer  poles  of  the  circuit  breaker  connect  to  the  positive 
equalizer  and  the  negative  equalizer  busses,  while  the  two  middle 
poles  connect  to  the  positive  main  bus  and  the  negative  bus. 
When  the  breaker  operates  through  overload  or  reversal,  all  four 
poles  trip  out  at  once,  thus  opening  the  positive,  positive  equa- 
lizer, negative  and  negative  equalizer  circuits. 

Electric  Operation. — Where  it  is  feasible  to  furnish  an  electri- 
cally operated  breaker  located  right  at  the  machine,  a  2-pole 
breaker  is  frequently  furnished  for  connecting  in  the  armature 
leads.  Such  a  breaker  completely  opens  up  the  generator  arma- 
ture circuit,  but  will  normally  leave  the  series  coils  connected 


326         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

across  between  the  positive  and  positive  equalizer  bus,  the  nega- 
tive and  the  negative  equalizer  bus. 

Neutral  Lead. — With  most  3-wire  generators  the  neutral 
lead  is  obtained  from  the  neutral  point  of  an  auto  transformer 
or  balance  coil  connected  across  two  collector  rings.  This 
neutral  is  normally  grounded  and  frequently  no  switches  what- 
ever are  furnished  for  use  in  the  neutral  circuit. 

SPECIAL  ISOLATED  PLANT  SWITCHBOARDS 

In  isolated  plants,  factories,  or  large  office  buildings  the  design 
of  the  switchboard  is  frequently  based  on  specifications  issued  by 
the  consulting  engineer  or  architect,  and  these  very  seldom  follow 
out  the  designs  that  have  been  standardized  by  the  larger  manu- 
facturing companies. 

Such  isolated  plant  switchboards  as  a  rule  control  a  com- 
paratively large  number  of  feeder  circuits,  and  it  becomes  neces- 
sary to  control  a  number  of  feeders  from  each  panel,  such  an 
arrangement  usually  resulting  in  a  special  design  of  switchboard 
for  each  individual  case. 

Walker  Switchboard. — Fig.  201  shows  a  fine  example  of  a 
switchboard  of  this  type  built  by  the  Walker  Electric  Company, 
and  installed  in  the  plant  of  the  Curtis  Publishing  Company,  of 
Philadelphia. 

This  switchboard  utilizes  Cutter  circuit  breakers,  Weston 
vertical  edgewise  group  mounted  feeder  ammeters,  Weston 
flush  mounted  illuminated  dial  instruments  and  controls  the 
output  of  eight  2-wire,  250- volt  generators  and  two  3-wire 
balancers,  the  total  generating  capacity  being  approximately 
3000  K.W. 

An  eight  section  control  desk  located  in  front  of  the  switch- 
board controls  the  generators  and  is  provided  with  flush  mounted 
illuminated  dial  Weston  ammeters  and  the  control  switches  for 
the  electrically  operated  generator  breakers,  the  motor  operated 
field  rheostat,  etc.  The  control  desk  as  well  as  the  panel  board 
is  of  gray  marble. 

The  panel  board  is  made  up  of  one  station  panel,  two  balancer 
panels,  five  lighting  and  six  power  panels.  Each  of  these  lighting 
and  power  panels  controls  six  circuits,  so  that  there  are  a  total 
of  66-2- wire  feeders  controlled  from  this  board,  each  equipped 
with  a  2-pole  circuit  breaker  and  an  ammeter.  Knife  switches 


LARGE  PANEL  SWITCHBOARDS 


327 


328         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

are  entirely  absent  from  the  switchboard  with  the  exception  of 
those  required  for  the  three  wire  balancers. 

As  the  circuit  breakers  in  the  feeder  circuits  embody  the  non- 
closable  on  overload  feature,  no  switches  are  needed  in  series  with 
them. 

Short  Circuit  Conditions. — For  light  and  power  service  at  250 
volts  in  plants  of  moderate  capacity,  particularly  when  fed  from 
D.C.  generators  in  place  of  synchronous  converters,  the  short-cir- 
cuit conditions  on  the  carbon  breakers  are  not  so  severe,  and  the 
resulting  arc  is  not  as  intense  as  encountered  in  railway  sub- 
stations of  large  capacity  operated  from  synchronous  converters. 

Carbon  break  circuit  breakers  can,  therefore,  be  utilized  to 
advantage,  placed  one  above  the  other  on  switchboard  panels  for 
this  class  of  service,  whereas  for  railway  work  it  becomes  almost 
essential  to  locate  them  at  the  top  of  a  panel  so  that  the  resulting 
arc  cannot  damage  the  panel  and  will  have  ample  space  in  which 
to  extinguish  itself. 

Circuit-Breaker  Protection. — Single  bus  railway  panels  pro- 
vide automatic  overload  protection  in  one  side  of  the  circuit  only; 
namely,  in  the  positive  side,  opposite  the  series  field.  This  pro- 
tection is  sufficient  for  synchronous  converters  with  overload 
protection  on  the  alternating-current  side  and  for  motor  driven 
generators  with  overload  protection  in  the  motor  circuit. 

Engine  Generators. — There  is  a  possibility  in  using  this  single 
protection  with  engine  driven  railway  generators  having  the  nega- 
tive lead  grounded,  that  the  circuit  breaker  in  the  positive  side 
does  not  protect  the  generator  against  possible  damage  due  to  a 
ground  either  in  the  machine  or  on  the  positive  side  between  the 
machine  and  circuit  breaker.  An  additional  circuit  breaker 
mounted  on  a  pedestal  and  installed  in  the  negative  armature 
lead,  is  required  by  the  National  Board  of  Fire  Underwriters. 
This  breaker,  when  provided,  has  an  auxiliary  switch,  so  that 
upon  the  opening  of  the  breaker,  the  switch  will  act  in  connection 
with  the  low  voltage  release  mechanism  of  the  positive  breaker 
and  cause  it  to  open.  It  is  recommended  that  the  negative 
breaker  be  set  higher  than  the  positive  breaker  on  the  switch- 
board and  thus  permit  the  latter  breaker  to  take  care  of  the 
ordinary  overloads. 

Converters  &  M.G.  Sets. — Direct-current  panels  for  synchron- 
ous converters  and  motor  generators,  2- wire  or  3-wire  D.C. 
service,  regularly  include  a  reverse-current  relay  operated  from 


LARGE  PANEL  SWITCHBOARDS  329 

the  ammeter  shunt,  in  addition  to  the  low  voltage  release  mech- 
anism supplied  with  the  direct-current  circuit  breaker.  An 
A.C.  low  voltage  coil  is  supplied  on  converter  panels  and  a  D.C. 
low  voltage  coil  on  generator  panels.  For  3-wire  service  one 
reverse-current  relay  or  attachment  will  be  found  sufficient 
in  all  cases  except  when  it  is  possible  that  battery  charging  may  be 
done,  at  times,  from  one  side  of  the  circuit  only.  In  this  case, 
two  reverse-current  relays  are  necessary  for  absolute  protection. 

Two  Wire. — Two-wire  light  and  power  panels  provide  auto- 
matic overload  protection  in  only  one  side  of  the  circuit,  namely, 
in  the  positive  side  opposite  the  series  field.  This  is  approved 
as  sufficient  protection  by  the  National  Board  of  Fire  Under- 
writers. 

Three  Wire. — Three- wire  light  and  power  panels  are  required 
by  the  National  Safety  Code  to  operate  with  the  neutral  grounded. 
They  provide  complete  automatic  overload  protection  on  both 
sides  of  the  machine.  Except  with  three  wire  booster  converters, 
which  are  shunt  machines,  a  2-pole  carbon  circuit  breaker  with 
equalizer  contacts  is  regularly  furnished  by  the  Westinghouse 
Company  for  machines  of  guaranteed  capacity  of  2000  amperes 
and  below  for  one  or  more  hours.  For  machines  of  larger 
capacities  a  4-pole  breaker  is  regularly  furnished  consisting  of 
a  positive  and  negative  pole  of  capacity  suitable  for  the  ma- 
chine, and  two  equalizer  poles  of  approximately  half  the  capacity 
of  the  main  poles.  The  Westinghouse  breaker  is  tripped  through 
overload  relays,  operated  from  the  ammeter  shunts  located  on 
the  generators  and  connected  in  the  circuit  between  the  armature 
and  the  equalizer  leads. 

Three  wire  booster  converters  have  no  compound  windings  and 
their  panels  are  furnished  with  an  overload  automatic  2-pole 
carbon  breaker.  No  overload  relays  are  necesary,  and  the  am- 
meter shunts  are  mounted  on  the  panel. 

Panels  controlling  the  direct-current  side  of  a  synchronous 
converter  or  motor  generator  have  the  circuit  breaker  equipped 
with  a  low  voltage  release  mechanism  having,  an  A.C.  coil  for 
converters  and  a  D.C.  coil  for  generators,  to  open  the  breaker 
by  the  operation  of  the  speed  limit  device  when  furnished  and  to 
provide  means  of  tripping  the  direct-current  breaker  upon  the 
opening  of  the  alternating-current  breaker. 

Meters. — Round  pattern  polarized  ammeters  and  voltmeters 
are  regularly  furnished  with  these  panels.  Illuminated  dial 


330         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

instruments  may  be  substituted.  The  full  scale  of  ammeters 
corresponds  approximately  to  the  momentary  overload  guarantee 
of  the  machine. 

Reactive  factor  meters  are  supplied  by  the  Westinghouse 
Company  with  synchronous  converter  D.C.  panels.  They  give 
an  emphatic  indication  of  the  idle  component  of  the  volt  am- 
peres. These  instruments  are  single  phase  and  will  indicate  the 
reactive  factor  of  one  phase  of  the  6-phase  synchronous  con- 
verter. As  the  phases  are  balanced,  this  is  sufficient  for  all 
operating  conditions. 

The  General  Electric  Company  furnish  a  reactive  volt  ampere 
indicator  reading  reactive  K.V.A.  for  the  same  service. 


AC.  Line 


Am  Shunt 


Storting 
Switch 


Kheo 


FIG.  202. — Diagram  of  D.C.  starting  of  synchronous  converters. 


D.C.  Starting. — When  D.C.  starting  of  motor  driven  generators 
and  synchronous  converters  is  desired,  the  standard  panels  must 
be  modified.  The  purpose  of  these  additions  is  shown  in  the 
diagram,  Fig.  202.  The  single-throw  auxiliary  switch  is  open 
when  the  main  switch  is  open.  This  switch  opens  the  tripping 
circuit  of  the  reverse-current  relay  during  starting,  making  it 
impossible  for  the  reverse-current  relay  to  trip  the  alternating- 
current  breaker  until  synchronizing  has  been  done  and  the  direct- 
current  voltage  adjusted,  so  that  the  machine  when  switched  in 
will  operate  in  the  normal  direction.  The  auxiliary  switch  is 
also  in  series  with  the  auxiliary  switch  of  the  alternating-current 


LARGE  PANEL  SWITCHBOARDS  331 

automatic  breaker  and  opens  the  interlock  connection  with  the 
direct-current  breaker,  so  that  the  latter  can  be  closed  for 
starting  while  the  alternating-current  breaker  is  in  the  open 
position. 

The  equalizer  switch  is  double  throw  to  cut  out  the  series  field 
in  starting. 

A.C.  Panels. — The  panels  used  for  the  control  of  the  A.C.  end 
of  synchronous  converters  and  their  transformers  are  usually 
made  to  line  up  with  the  D.C.  panels. 

Protection. — Automatic  protection  on  the  alternating- current 
side  of  the  synchronous  converter  is  provided  on  the  high  tension 
side  of  the  step  down  transformer  by  an  instantaneous  overload 
oil  circuit  breaker,  tripped  from  current  transformers.  The 
breaker  is  also  equipped  with  low  voltage  release  and  auxiliary 
switch.  A  low  voltage  trip  instantaneous  overload  carbon  circuit 
breaker  is  provided  for  the  direct-current  side.  In  the  majority 
of  railway  applications  involving  capacities  of  1000  K.W.  and 
below  it  is  advisable  to  eliminate  the  overload  feature  on  the  D.C. 
breaker.  The  low  voltage  coil  of  the  direct-current  breaker  is 
connected  to  the  low  tension  transformer  leads  in  parallel  with 
the  low  voltage  coil  of  the  A.C.  breaker.  The  speed-limit  switch 
furnished  with  and  mounted  on  the  converter,  opens  upon  over- 
speed  and  causes  both  A.C.  and  D.C.  breakers  to  trip  simultane- 
ously. 

The  low  voltage  coil  on  the  D.C.  breaker  is  also  actuated  by  an 
auxiliary  switch  that  is  always  provided  on  the  oil  circuit  breaker 
so  that  when  this  breaker  opens,  the  direct-current  breaker  also 
opens,  thus  providing  against  motoring  from  direct-current 
power  and  eliminating  the  liability  of  reversal  in  polarity  on 
compound  wound  machines.  Reverse-current  relays  are  also 
provided  on  the  D.C.  panel,  arranged  to  open  the  alternating- 
current  breaker  upon  reversal  of  direct-current  power,  which  in 
turn  opens  the  direct-current  breaker.  The  reverse-current 
relay  may  be  omitted  only  if  the  converter  is  not  interconnected 
with  an  independent  source  of  direct-current  power,  so  that  there 
can  be  no  reversal  upon  the  interruption  of  the  alternating-cur- 
rent supply. 

Transformers. — transformer  primary  circuit-breaker  equip- 
ments constitute  part  of  the  complete  switchboard  equipment 
for  the  control  of  alternating-current  self-starting  synchronous 
converters. 


332         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

These  equipments  usually  comprise  one  3-pole,  single- 
throw  instantaneous  overload,  automatic  oil  circuit  breaker,  of 
one  of  the  following  types: 

1.  Hand  operated,  remote  mechanically  operated,  instantane- 
ous overload,  automatic  oil  circuit  breaker,  complete  with  two 
5-ampere  trip  coils,  low  voltage  release  mechanism  coil  and  hand- 
reset  device  and  auxiliary  contact  to  interlock  with  D.C.  breaker. 

2.  Electrically   operated    125-volt   D.C.    control,   oil     circuit 
breaker,  with  two  5-ampere  trip  coils  at  breaker,  instantaneous 
overload. 

In  case  inverse  time  element  is  desired  with  the  breaker  equip- 
ment, two  overload  relays  may  be  added  to  the  electrically 
operated  circuit  breaker.  With  the  remote  manually  operated 
oil  circuit  breakers  only,  inverse  time  element  attachments 
can  be  furnished  with  the  circuit  breaker. 

Starting  Panels. — These  provide  for  the  starting  switch  equip- 
ment for  alternating-current  self -starting  converters.  They  are 
in  addition  to  the  converter  panel. 

The  starting  panels  for  th.e  600-volt  converters  often  include 
equalizer  and  negative  switches.  When  the  relative  location  of 
the  apparatus  in  the  station  is  such  that  it  is  not  desirable  to 
run  the  equalizer  and  negative  cables  to  the  starting  panel,  a 
separate  pedestal  with  proper  equalizer  and  negative  switches 
may  be  used. 

Starting  Switch. — These  starting  panels  usually  have  mounted 
on  them  a  3-pole  double-throw  knife  switch  to  connect  the  con- 
verter to  low  voltage  for  starting  and  full  voltage  for  running  as 
well  as  a  2-pole  double-throw  switch  for  field  reversing  in  case 
machine  comes  up  to  speed  with  the  incorrect  polarity. 

When  the  synchronous  converter  is  used  for  3-wire  D.C.  service 
an  auxiliary  blade  is  furnished  on  the  starting  switch  and  extra 
contacts  furnished  so  that  in  the  running  position  the  neutral  of 
the  D.C.  system  is  connected  to  the  neutral  point  on  the  low 
tension  windings  of  the  various  transformers.  Figure  203 
shows  the  connections  of  a  typical  synchronous  converter 
installation  for  3-wire  D.C.  service. 

1500  Volt  D.C.— Where  the  D.C.  panels  are  intended  for  1200- 
1500-volt  service,  the  carbon  breakers  and  knife  switches  are 
made  distant  control  and  the  panels  arranged  as  shown  in  Fig. 
204.  These  panels  are  intended  for  use  with  two  generators  or 
converters  operating  in  series  and  each  panel  consists  of  three  sec- 


LARGE  PANEL  SWITCHBOARDS 


333 


3  Phase  Incoming 

Note' -Switchboard  Conn-  Line 

ections  ore  shown  as 


Ground 
' 


FIG.  203. — Diagram  of  connections  for  D.C.  three-wire. 


334         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


tions  2  inches  thick  with  3^-inch  bevels;  the  lower  section  is  25 
inches  high,  the  middle  section  45  inches  high,  and  the  upper 
section  30  inches  high.  They  are  mounted  on  angle  iron  frame 
with  channel  iron  base.  The  total  height  of  the  panel  including 
the  base  is  102  inches.  The  barriers  provided  between  the  circuit 
breakers  and  at  the  ends  extend  14  inches  above  the  top  of  the 
panel.  No  high  voltage  live  parts  are  mounted  within  7  feet  of 
the  floor  on  the  front  of  the  panels. 

The  starting  switch  and  the  field  discharge  switch  on  the  front 


ED 


00 


ED 


0 


0 


0 


of  the  starting  panels  are  pro- 
vided with  barriers  to  protect 
against  accidental  contact 
with  live  parts. 

Meters.  —  The  instruments 
included  with  these  panels  in 
the  direct-current  circuits 
have  live  parts  insulated  from 
the  case  for  full  voltage  and 
cases  grounded. 

Reactive  factor  meters  or 
power  factor  meters  are  sup- 
plied for  synchronous  con- 
verters as  an  aid  in  adjusting 
the  field  properly  to  keep 
down  the  losses  in  the  ma- 
chine armatures.  These 
losses  are  less,  the  more  nearly 

the  synchronous  converter  operates  at  zero  reactive  factor. 
The  reactive  factor  meter  is  connected  in  the  low  voltage  leads 

to  the  converter  and  not  on  the  high  voltage  side  of  the  step  down 

transformers  in  order  that  it  will  indicate  the  true  condition  in 

the  converter  armature. 

Synchronous  motor  panels  are  supplied  with  a  main  ammeter 

and  a  field  ammeter  for  indicating  proper  machine  operation. 
Rheostats.  —  When  two  machines  are  connected  in  series  for 

1200-volt  operation,  their  two  rheostats  are  operated  in  tandem  as 

one  circuit  from  a  single  hand  wheel.     An  insulated  sprocket  wheel 

is  furnished  on  each  rheostat  so  that  the  operating  mechanism 

is  insulated  from  live  parts. 

Circuit  Breakers.  —  The  positive  circuit  breakers  are  mounted 

on  the  front  and  at  the  top  of  the  panels  and  are  operated  by 


FIG.  204. — Switchboard  for  1500-volt 
D.C.  railway. 


LARGE  PANEL  SWITCHBOARDS 


335 


closing  and  tripping  handles  located  at  a  convenient  height  on  the 
middle  panel  section.  The  circuit  breakers  trip  free  of  the  closing 
mechanism  so  that  the  speed  of  opening  is  the  same  as  for  direct 
operated  breakers.  The  closing  and  tripping  mechanisms  are 
insulated  from  the  breaker. 


Note  -Switchboard  Conn- 
ections oresho»>n  as 
viewed  Irotn  rear  of  6oonf 


J  Phase  Incoming 
Line 


Supplied  only  on 
Specifications 

Commutotinq  / 
FIQ.  205. — Diagram  of  connections  for  1500-volt  D.C.  railway. 

The  installation  of  negative  machine  circuit  breakers  is  opti- 
onal. They  provide  additional  protection  against  grounds  caused 
by  flash-over  or  insulation  failure.  In  standard  practice  the 
circuit  breakers  in  the  alternating-current  supply  circuits  are 
depended  upon  to  provide  this  protection.  The  negative  breakers 
are  direct-operated,  being  located  at  a  convenient  height  on 
pedestals.  The  moving  parts  of  the  negative  breakers  are  dead 
when  the  breakers  are  open. 

Switches. — The  positive  switches  are  mounted  on  bases  on  the 
rear  of  the  panels,  with  Westinghouse  construction,  or  on  the 


336         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

front  top  section  alongside  of  the  circuit  breaker  for  General 
Electric  construction,  the  lowest  point  of  live  parts  being  at  least 
7  feet  above  the  floor,  and  are  operated  from  handles  on  the  front, 
located  at  a  convenient  height  and  in  line  with  the  circuit-breaker 
handles.  The  operating  mechanism  is  rigidly  connected  to  the 
switch  so  that  the  position  of  the  handle  on  the  front  is  always 
a  true  indication  whether  the  switches  are  open  or  closed. 

Switches. — The  switches  for  the  negative  side  of  the  machine 
set  are  direct-operated.  These  are  of  the  600- volt  type  and  are 
provided  with  barriers  when  connections  are  such  that  atten- 
dants would  otherwise  be  exposed  to  a  dangerous  voltage.  Nega- 
ive  and  equalizer  apparatus  may  be  omitted,  if  desired,  when 
the  station  will  have  but  a  1200-volt  converter  or  generator  set, 
as  they  are  not  essential  for  the  operation  of  a  single  set.  A  nega- 
tive main  switch  is  convenient  as  a  means  of  disconnecting  the 
machine  from  the  ground  for  insulation  testing. 

Connections. — Fig.  205  shows  the  connections  of  a  typical 
substation  for  the  control  of  a  13,200-volt  3-phase  incoming 
line  and  two  6-phase  synchronous  converters,  self-starting  from 
the  A.C.  side  and  operating  in  series  on  the  D.C.  side  for  1200- 
1500- volts  D.C.  railway  service. 

AUTOMATIC  SUBSTATIONS 

For  many  synchronous  converter  substations,  particularly  for 
interurban  railway  work,  automatic  operation  has  been  adopted. 
Very  complete  and  ingenious  arrangements  of  apparatus  have 
been  worked  out  by  the  engineers  of  the  General  Electric  Company 
and  the  Westinghouse  Electric  &  Manufacturing  Company. 
The  first  automatically  controlled  railway  substation  was 
equipped  by  the  General  Electric  Company  and  placed  in  service 
during  December,  1914,  on  the  Elgin  and  Belvedere  Electric 
Railway.  The  following  description  has  been  taken  from  a  paper 
by  Mr.  Frank  Peters,  of  the  General  Electric  Company,  presented 
before  the  Pittsburgh  Meeting  of  the  A.I.E.E.,  March  14,  1920. 

G.  E.  Schemes. — The  type  of  automatic  equipments  supplied 
by  the  General  Electric  Company  consists  of  a  group  of  relays, 
grid  resistors  and  standard  contactors,  which  together  with  a 
motor  driven  drum  controller  perform  the  usual  function  of 
starting,  stopping  and  protecting  the  machines  against  irregu- 
larities without  the  aid  of  an  attendant.  In  general,  relays  are 


LARGE  PANEL  SWITCHBOARDS 


337 


used  where  the  functions  of  starting,  stopping  and  protecting  the 
machines  depend  upon  voltage,  current  or  independent  time 
values.  During  starting  and  stopping,  however,  numerous  opera- 
tions must  be  performed  in  a  definite  sequence,  which  if  not 
strictly  adhered  to,  is  conducive  to  service  interruptions. 

Controller. — The  motor  driven  drum  controller  is  used  to  ob- 
tain this  fixed  time  relation  of  events  and  to  substitute,  wherever 
possible,  a  type  of  contact  more  substantial  than  can  be  used  with 


FIG.  206. — General    Electric  Co.   motor  driven  controller  for  automatic  sub- 
station. 

relays.  This  device  also  includes  a  small  D.C.  generator  which 
at  the  proper  time  during  the  starting  operation  separately  ex- 
cites the  converter  field,  thereby  definitely  and  immediately  in- 
suring the  correct  polarity. 

Duties. — Protective  devices  having  the  following  duties  are 
provided  to  perform  the  functions  ordinarily  left  to  the  discre- 
tion of  the  operator. 

1.  To  limit  the  overloads. 

2.  To  limit  the  temperatures. 

3.  To  shut  down  the  machine. 

(a)  When  A.C.  or  continuous  D.C.  short  circuits  occur. 
(6)  Upon  failure  of  alternating  current. 

(c)  Upon  failure  of  any  device. 

(d)  In  case  of  excessive  speed. 

(e)  Upon  reversal  of  direct  current. 

4.  To  prevent  machine  starting. 

(a)  During  low  A.C.  voltage. 

(b)  During  single-phase  A.C.  supply. 

Connections. — By  referring  to  Fig.  207  which  is  a  typical 
wiring  diagram  of  an  automatic  500-K.W.  600- volt  equipment,  the 


338         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

-i! 


LARGE  PANEL  SWITCHBOARDS  339 

sequence  of  operation  may  be  followed.  For  convenience  of 
reference  the  principal  devices  have  been  numbered  or  otherwise 
labeled.  It  will  be  noted  that  the  220-volt  A.C.  control  bus  is 
continuously  excited  from  the  control  transformer  No.  1 1  and  the 
operating  coil  of  contact-making  voltmeter  No.  1  is  always 
connected  between  trolley  and  ground. 

Starting. — Assuming  a  particular  station  is  shut  down  and  a 
train  is  approaching.  As  it  increases  its  distance  from  the  next 
station  on  the  line  it  will  eventually  cause  the  trolley  voltage  to 
drop  and  at  a  predetermined  value,  usually  450  volts,  contact- 
making  voltmeter  No.  1  opens,  de-energizing  the  operating  coil 
of  relay  No.  2,  which  had  been  previously  held  open  by  excita- 
tion from  the  220-volt  A.C.  control  bus  through  relay  No.  1. 
The  closing  of  No.  2  closes  relay  No.  3  causing  it  to  pick  up  and 
close  contactor  No.  4  provided  the  hand  reset  switch  and  contacts 
of  A.C.  low  voltage  relays  No.  27  are  closed.  Relay  No.  2  has 
a  dashpot  to  prevent  momentary  fluctuation  of  low  voltage  from 
producing  false  operations  of  the  machine.  With  the  drum 
controller  No.  34  in  the  "off"  position  as  would  be  the  case  before 
the  machine  starts,  contactor  No.  4  completes  a  circuit  through 
segments  No.  13  and  No.  16  on  the  drum  controller  and  the 
limit  switch  of  the  brush-raising  device  which  closes  contactor 
No.  6,  thereby  starting  rotation  of  the  motor  driven  drum  con- 
troller. Controller  segment  No.  15  soon  closes  contactor  No.  5 
which  in  turn  energizes  the  motor  operated  oil  switch  mechanism 
causing  the  main  converter  transformers  to  become  energized  by 
the  closing  of  oil  circuit  breaker  No.  7.  The  operating  coil  con- 
nection of  contactor  No.  5  is  then  transferred  from  segment  No. 
15  to  No.  14.  This  circuit  passes  through  an  auxiliary  switch  on 
the  oil  circuit  breaker  to  insure  the  return  of  all  devices  to  their 
normal  position  should  the  breaker  open  for  any  reason.  When 
segment  No.  2  makes  contact,  starting  contactor  No.  10  is  closed 
connecting  the  converter  to  the  low  voltage  taps  provided  the 
A.C.  supply  is  delivering  3-phase  current  as  determined  by 
relay  No.  32.  Shortly  the  drum  controller  stops  rotating  be- 
cause of  the  gap  in  segment  No.  16  and  waits  if  necessary  for  the 
converter  to  come  up  to  speed.  At  approximately  synchronism, 
speed-control  switch  No.  13  closes,  bridging  by  aid  of  segment 
No.  20  the  gap  in  segment  No.  16,  causing  the  controller  again  to 
start  rotating  so  as  to  complete  the  function  of  connecting  the 
machine  to  the  line. 


340         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Next  segment  No.  3  closes  contactor  No.  31  connecting  to  the 
converter  fields  a  250-volt  supply  obtained  from  the  small  gen- 
erator on  the  drum  controller,  thereby  immediately  ensuring  proper 
polarity.  Contactor  .No.  31  is  then  opened  by  segment  No.  3 
and  the  self-exciting  field  contactor  No.  14  closed  by  segment  No. 
4  and  running  contactor  No.  16  closed  by  segment  No.  5 
connecting  the  converter  to  normal  secondary  A.C.  voltage. 
Starting  and  running  contactors  No.  10  and  No.  16  are  both  mechan- 
rically  and  electrically  interlocked  with  respect  to  one  another 
to  insure  against  accidentally  short-circuiting  a  portion  of  the  trans- 
former secondary  winding.  Segment  No.  26  next  starts  the 
motor  operated  brush  rigging  causing  the  converter  brushes  to 
be  lowered,  which  completes  the  operation  of  preparing  the  ma- 
chine for  connection  to  the  D.C.  bus.  Segment  No.  7  is  next 
energized  with  600  volts  direct  current  and  shortly  thereafter 
segment  No.  8  closes  the  D.C.  line  contactor  No.  18  whose  con- 
trol circuit  is  in  series  with  converter  field  relay  No.  30,  polarized 
relay  No.  36  and  auxiliary  switches  on  running  contactor  No. 
16  and  control  contactor  No.  4,  thereby  ensuring  before  closing 
No.  18  that  the  converter  has  proper  polarity,  correct  field  and 
full  voltage  A.C.  running  connections. 

As  soon  as  the  line  contactor  closes  the  machine  delivers  load 
to  the  bus  through  the  load  limiting  resistors  which,  however, 
are  soon  short-circuited  by  contactors  No.  20  and  No.  21  opera- 
ted by  segments  No.  9  and  No.  10.  The  drum  controller  is  then 
stopped  by  segment  No.  17.  When  connection  to  the  bus  is 
made  through  No.  18  the  flow  of  current  closes  relay  No.  37, 
which  will  cause  relay  No.  3  to  remain  closed  regardless  of  relay 
No.  1  whose  function  started  the  station.  In  other  words  the  con- 
trol of  the  station  is  now  dependent  on  the  contacts  of  No.  37 
which  will  remain  closed  so  long  as  a  predetermined  current  is 
being  delivered  to  the  bus.  Should  the  current  fall  below  a  set 
value,  relay  No.  37  will  open  and  cause  relay  No.  3  to  drop  out 
after  a  certain  period  of  time  and  shut  down  the  station.  Relay 
No.  3  has  a  dashpot  and  is  timed  so  that  momentary  low  values 
of  current  causing  No.  37  to  open  will  not  shut  down  the  equip- 
ment. 

Shutting  Down. — When  the  station  does  shut  down,  relay  No. 
3  opens  contactor  No.  4  causing  running  contactor  No.  16  and 
D.C.  line  contactor  No.  18  to  drop  out  and  disconnect  the  ma- 
chine. Contactor  No.  5  opens  after  contactor  No.  4  which 


LARGE  PANEL  SWITCHBOARDS  341 

operation  establishes  through  an  auxiliary  contact  a  circuit  to 
contactor  No.  6,  thereby  starting  the  controller  and  running  it 
to  its  "off"  position.  While  doing  this,  however,  segment  No. 
24  trips  out  the  oil  circuit  breaker  and  segment  No.  25  causes 
the  converter  brushes  to  be  raised  in  preparation  for  starting 
upon  the  next  load  demand. 

Overload. — In  the  event  a  heavy  D.C.  overload  occurs,  relay 
No.  24  will  pick  up  and  open  contactor  No.  20,  thereby  inserting 
resistance  in  the  circuit.  Should  the  overload  increase  to  a 
greater  value,  relay  No.  25  will  operate  and  insert  more  resist- 
ance, and  in  stations  not  provided  with  individual  feeder  pro- 
tection a  third  step  of  resistance  is  provided  to  limit  still  greater 
overload  demands.  The  value  of  resistance  used  is  such  as  to 
permit  short  circuit  in  the  immediate  vicinity  of  the  station  with- 
out injuring  the  machine.  In  some  stations  individual  feeder 
protection,  which  consists  of  an  overload  relay  No.  23,  a  contactor 
No.  19  and  a  resistor  in  each  feeder  circuit,  is  installed,  there- 
by localizing  to  a  degree  the  function  of  overload  protection  to 
each  feeder.  With  such  an  arrangement  only  two  sections  of 
resistance  are  used  in  the  machine  circuit. 

Overheating. — Protection  from  overheating  the  machine,  its 
bearings  and  load  limiting  resistors  is  obtained  by  use  of  tempera- 
ture relays  No.  38  and  No.  33  arranged  to  shut  down  the  station 
immediately  should  such  a  condition  arise. 

Reversal. — A  reversal  of  direct  current  is  prevented  by  relay 
No.  29  and  overspeed  by  speed-limit  switch  No.  12-A.  Both 
of  these  devices  necessarily  operate  a  control  circuit  which  im- 
mediately opens  contactor  No.  4  and  shuts  down  the  station. 
A  shunt  trip  hand  operated  D.C.  circuit  breaker  No.  15  is  in 
series  with  No.  18  and  only  used  to  protect  against  the  possi- 
bility of  the  line  contactor  freezing  closed.  Should  this  condi- 
tion occur  the  converter  would  motor  from  the  D.C.  end  upon 
the  A.C.  end  being  disconnected  and  the  excessive  speed  result- 
ing would  trip  the  circuit  breaker  No.  15  through  the  operation 
of  speed  switch  No.  12. 

Short  Circuit. — In  case  a  short  circuit  occurs  on  the  A.C.  side 
of  the  equipment,  the  definite  time  limit  overload  relay  No.  28 
will  trip  out  the  main  oil  circuit  breaker,  shutting  down  the 
station  and  at  the  same  time  opening  the  hand  reset  switch  which 
necessitates  reclosing  by  hand  before  the  station  can  be  started 


342         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

again.  This  feature  insures  an  inspector  visiting  the  station 
to  investigate  the  cause  of  the  serious  A.C.  overload. 

Low  A.C.  voltage  relay  No.  27  which  is  calibrated  for  a  definite 
value,  is  connected  so  as  not  to  permit  the  station  to  start,  or  to 
shut  it  down  if  running,  should  the  high  tension  voltage  become 
so  low  as  to  interfere  with  proper  operation. 

If  for  any  reason  a  single-phase  condition  exists  on  the  second- 
ary side  of  the  transformer  during  starting  operations,  relay  No. 


FIG.   208. — General  Electric  Co.  automatic  substation  with  M.G.  set. 


32  will  lock  out  starting  contactor  No.  10  and  prevent  the  con- 
verter from  being  connected  to  the  transformer. 

Polarized  relay  No.  36  protects  against  the  possibility  of  the 
machine  ever  being  connected  to  the  line  in  the  reverse  direction. 
Unless  proper  polarity  has  been  established  before  connecting 
the  machine  to  the  bus,  line  contactor  No.  18  will  not  close. 

Motor  Generator. — In  stations  containing  a  motor-generator 
set  instead  of  a  synchronous  converter,  certain  modifications  to 
the  equipment  are  necessary  to  accommodate  the  starting  opera- 
tions, but  the  scheme  of  operation  with  few  exceptions  is  similar 
to  the  converter  equipments.  Oil  immersed  starting  and  running 
contactors  are  used  because  of  the  higher  transformer  secondary 


LARGE  PANEL  SWITCHBOARDS  343 

voltage  and  a  certain  amount  of  overload  protection  is  obtained 
by  inserting  one  or  two  steps  of  resistance  in  the  generator  field 
circuit  in  addition  to  two  steps  of  series  resistance  in  the  main 
D.C.  circuit.  This  arrangement  reduces  initial  cost  since  the  field 
resistance  and  its  contactors  are  of  small  capacity.  An  energy 
saving  in  resistor  heat  loss  is  also  accomplished.  The  250- volt 
generator  on  the  drum  controller  becomes  unnecessary  in  the 
case  of  a  motor  generator  automatic  equipment.  See  Fig.  208 
for  automatic  substation  with  motor-generator  set. 

Westinghouse  Schemes. — The  automatic  substation  equip- 
ment of  the  Westinghouse  Electric  &  Manufacturing  Company 
has  been  designed  to  duplicate  in  every  way  the  manual  operation 
of  substation  apparatus  without  the  attention  of  an  operator. 
Starting  and  shutting  down  of  the  station  are  functions  of  the 
load  demand.  In  addition,  many  protective  devices  uncommon 
to  the  average  substation  give  absolute  protection  which  is  free 
from  the  human  element.  The  schematic  diagram  Fig.  209 
applies  to  equipment  for  standard  alternating-current,  self- 
starting  synchronous  converters  up  to  and  including  1500- 
kilowatt  capacity,  750-volts  direct-current.  Referring  to  this 
diagram,  the  scheme  of  operation  is  as  follows: 

Starting. — A  car  or  train  enters  the  zone  of  a  station  which  is 
at  that  instant  idle.  As  the  train  approaches  the  station,  the 
trolley  voltage  at  the  station  is  reduced.  When  the  voltage 
falls  to  a  predetermined  value,  for  example  to  75  per  cent,  of 
normal  or  below,  contacts  of  a  direct-current  voltage  relay  (1) 
in  the  trolley  circuit  close,  and  as  a  result  the  coil  of  an  alternating- 
current  voltage  relay  (2)  is  energized,  through  an  interlock  on  the 
brush  lifting  device  (31),  closed  when  brushes  are  raised  from 
commutator.  At  the  end  of  a  definite  time  interval,  which  may 
be  adjusted  from  instantaneous  to  five  seconds,  the  contacts  of 
this  relay  close.  The  time  element  prevents  the  station  re- 
sponding to  momentary  reductions  in  D.C.  voltage,  and  in 
addition  prevents  the  station  from  starting  in  case  the  A.C. 
voltage  is  abnormally  low.  The  closed  contacts  of  A.C.voltage 
relay  (2)  complete  a  circuit  which  closes  the  master  relay  (3) 
thereby  energizing  an  auxiliary  control  bus  'A-2'.  Relay  (3) 
completes  its  own  holding  circuit,  making  further  functioning 
of  the  control  apparatus  independent  of  trolley  voltage. 

Energizing  of  auxiliary  control  bus  'A-2'  causes  oil  breaker 
(20)  to  close  through  the  functioning  of  its  control  contactor  (22). 


344         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

The  oil  breaker  in  the  closed  position  completes,  through  an 
interlock,  the  circuit  for  an  alternating-current  dashpot  relay 
(21)  which,  when  closed,  de-energizes  the  oil  breaker  control 


...  . 

SjftSiat          23  AC' Onload  Relay, 
24  Overspeed  Devree 


GridThrrrna  iConv'rt'r)   40-80  Feeder  Contacton 

mal  Kolay    41-81  DC  Feeder  Resisfnoe 
Lock-Out  Relay  Shunting  Contacton 


FIG.  209. — Diagram  of  connections  Westinghouse  automatic  substation. 

contactor  (22).  The  oil  breaker  latches  closed  mechanically. 
In  addition,  bus  'A-2'  energized,  closes  shunt  relay  (4)  and 
field  contactor  (5).  The  closing  of  relay  (4)  in  turn  closes  alter- 
nating-current machine  starting  contactor  (6)  which  connects 


LARGE  PANEL  SWITCHBOARDS 


345 


the  converter  to  the  starting  taps  of  the  power  transformers.  It 
will  be  noted  that  the  closing  of  relay  (4)  and  contactor  (5) 
also  completes  the  circuit  for  a  polarized  motor  which  drives  a 
rotary  switch  (7)  upon  which  is  mounted  four  pairs  of  contacts, 
(7a),  (7b),  (7c)  and  (7d). 

Rotary  switch  (7)  is  driven  by  a  D.C.  motor  having  a  perma- 
nent magnet  field  in  addition  to  the  ordinary  field  winding.  In 
starting,  field  coils  of  the 
motor  are  connected  to 
trolley  and  rail,  and  the 
armature  is  connected  to 
the  D.C.  brushes  of  the 
converter.  Until  the  con- 
verter pulls  into  step, 
alternating  current  is  de- 
livered to  the  motor  arma- 
ture causing  it  to  oscillate; 
when  the  converter  is  in 
step,  direct  current  is  de- 
livered to  the  armature 
causing  it  to  rotate  in  a 
direction  dependent  on  the 
polarity  of  the  converter. 
See  Fig.  210. 

Polarity. — Assuming  incorrect  polarity,  the  drum  of  (7)  re- 
volves in  a  counter  clockwise  direction.  Relay  (8)  closes  as 
contact  (7a)  is  made,  completes  its  own  holding  circuit  and  closes 
a  contact  in  series  with  the  coil  of  a  direct-current  relay  (9)  which 
closes  when  contact  is  made  at  (7d).  This  relay  completes  its 
own  holding  circuit,  opens  shunt  field  contactor  (5)  and  closes 
reverse  field  contactor  (10).  Relay  (8)  is  opened  by  the  shorting 
of  its  coil,  by  an  interlock  closed  when  reverse  field  contactor  (10) 
is  closed,  thus  permitting  the  rotary  switch  to  idle  over  the 
remaining  contacts.  The  converter  voltage  on  reverse  field  falls 
to  zero  thereby  de-energizing  direct-current  relay  (9)  which  in 
the  open  position  causes  reverse  field  contactor  (10)  to  open,  and 
normal  field  contactor  (5)  to  again  close.  This  operation  cor- 
rects polarity  under  normal  line  conditions;  however,  should 
reverse  polarity  persist,  the  above  operation  will  be  once  or  twice 
repeated  as  may  be  necessary.  In  extreme  cases,  it  is  very 
difficult  to  correct  polarity  by  field  reversal,  so,  should  the  third 


FIG.  210. — Westinghouse  rotary  drum 
switch  for  automatic  substation. 


346         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

attempt  fail,  relay  (4)  and  in  turn  starting  contactor  (6)  will  be 
opened  by  the  closing  of  the  contacts  of  the  field  reversal  limiting 
relay  (26).  This  relay  is  a  step  by  step  device  which  operates 
each  time  the  direct-current  relay  (9)  closes,  but  is  mechanically 
restored  to  first  position  when  alternating-current  starting  con- 
tactor (6)  opens.  The  alternating-current  starting  contactor  (6) 
remains  open  for  a  short  interval  dependent  on  the  time  element 
of  an  air  dashpot  which  at  the  end  of  its  travel  trips  open  the 
contacts  of  (26).  Relay  (4)  now  closes,  in  turn  reclosing  alter- 
nating-current starting  contactor  (6).  One  familiar  with  sub- 
station operation  will  appreciate  that  the  above  procedure 
automatically  duplicates  the  work  of  an  operator  correcting  for 
reversed  polarity. 

Assuming  correct  polarity,  drum  switch  (7)  rotates  in  a  clock- 
wise direction.  Relay  (8)  closes  as  contact  is  made  at  (7a), 
completes  its  own  holding  circuit  and  closes  contacts  in  series 
with  shunt  relay  (19)  which  closes  when  contact  is  made  at  (7b). 
Relay  (19)  closed,  forms  its  own  holding  circuit,  opens  relay  (4) 
which  in  turn  opens  alternating-current  contactor  (6).  The 
closing  of  relay  (19)  and  the  opening  of  contactor  (6)  closes  alter- 
nating-current running  contactor  (11)  thereby  connecting  the 
converter  with  correct  polarity  to  the  full  voltage  A.C.  circuit. 
Interlocks  opened  by  the  closing  of  (11)  de-energize  the  polarized 
motor  relay  (7). 

The  alternating-current  running  contactor  (11)  in  the  closed 
position,  through  the  closing  of  an  interlock,  energizes  the  brush 
lifting  device  (31)  by  which  the  direct-current  brushes  are 
lowered  into  position  on  the  converter  commutator.  An  inter- 
lock on  (31),  closed  when  brushes  are  in  the  running  position, 
completes,  through  an  interlock  on  the  alternating-current  run- 
ning contactor  (11),  a  circuit  which  closes  the  direct-current  line 
switch  (12)  thus  connecting  the  converter  to  the  trolley  through 
resistance  proportioned  to  limit  the  current  in  the  machine  to 
approximately  150  per  cent,  of  its  rated  full-load  capacity.  Re- 
sistance shunting  contactors  (14)  and  (15)  are  closed  by  the  direct- 
current  accelerating  relays  (12a)  and  (14a)  should  normal  load 
not  be  exceeded. 

Feeders. — Feeder  contactors  (40)-(80)  are  normally  closed, 
the  operating  coils  being  energized  from  the  trolley  circuit. 
Feeder  resistance  shunting  contactors  (80)-(81)  open  and  close 
dependent  on  current  setting  of  D.C.  series  relays  (40a)-( 


LARGE  PANEL  SWITCHBOARDS  347 

Assuming  overload  on  feeder  (41),  series  relay  (40a)  will  open 
contactor  (41)  thereby  inserting  resistance  in  series  with  the 
feeder.  Should  the  overload  be  severe  and  last  for  some  length 
of  time,  heat  from  the  series  resistance  will  open  the  contacts  of 
thermostat  (33)  thus  opening  contactor  (40),  thereby  isolating 
the  feeder  until  the  resistance  cools  to  a  point  which  will  allow  the 
contacts  of  thermostat  (33)  to  again  close.  If  the  sum  of  the 
feeder  loads  through  resistances  is  in  excess  of  the  safe  load  of  the 
converter,  resistance  shunting  contactors  (14)  and  (15)  also  open 
through  similar  action  of  (12a)  and  (14a). 

When  all  resistance  is  cut  out  of  the  circuit,  the  trolley  voltage 
at  the  station  rises  to  a  point  which  will  open  the  contacts  of 
voltage  relay  (1).  However,  since  the  master  relay  (3)  maintains 
its  own  holding  circuit,  no  action  results  from  fluctuations  of  the 
direct-current  voltage. 

Shutting  Down. — Shutting  down  of  the  station  is  dependent 
on  the  position  of  series  underload  relay  (13).  When  the  load 
on  the  converter  falls  to  or  below  a  predetermined  value,  the 
contacts  of  this  relay  close,  thereby  starting  the  underload  delay 
relay  (27). 

Relays. — Underload  delay  relay  (27)  consists  of  a  direct-cur- 
rent motor  driving,  through  a  train  of  gears  and  a  magnetic 
clutch,  a  vertical  shaft  mounting  a  small  arm  which,  at  the  end 
of  its  travel,  closes  a  pair  of  contacts  short-circuiting  the  coil  of 
the  master  relay  (3),  causing  it  to  drop  out,  thus  de-energizing 
the  auxiliary  control  bus  'A-2'  and  thereby  opening  all  alter- 
nating-current and  direct-current  contactors.  The  master  relay 
in  the  open  position  closes  an  interlock  which  energizes  the 
brush  lifting  device  (31)  and  the  brushes  are  raised  from  the 
commutator  to  the  starting  position.  Should  load  be  de- 
manded from  the  station  before  the  contacts  of  underload  delay 
relay  (27)  are  closed,  the  opening  of  the  contacts  of  series  relay 
(13)  de-energizes  the  motor  and  magnetic  clutch  in  series  with  it. 
The  shaft  releases  and  is  returned  to  its  starting  position  by 
means  of  a  small  coiled  spring,  thus  assuring  a  very  definite 
no-load  period.  Any  time  element  desired  between  the  limits 
of  3-and  30-minutes  may  be  secured  by  simple  adjustments. 

Reverse-phase  starting  and  single-phase  starting  are  prevented 
by  the  closing  of  the  contacts  of  reverse  phase  and  low  voltage 
relay  (18)  which  short-circuits  the  coil  of  the  master  relay  (3). 

Low  Voltage. — If  the  alternating  current  line  voltage  is  too 


348         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

low  for  satisfactory  operation,  relay  (2)  will  not  operate  and  the 
contacts  of  relay  (18)  close,  as  stated  in  the  above  paragraph, 
either  of  which  prevents  the  station  from  starting.  Should  low 
voltage  occur  while  the  station  is  in  operation,  the  contacts  of 
relay  (18)  close. 

Direct-Current  Overload. — Various  sections  of  the  current 
limiting  resistor  are  inserted  in  the  machine  circuits  by  con- 
tactors (14)  and  (15),  when  loads  exceed  the  setting  of  the  over- 
load trip  on  the  contactors.  When  the  current  values  are  within 
the  overload  setting  of  the  contactors,  they  again  reclose. 
Overload  settings  of  the  switches  and  the  ohmic  value  of  the  re- 
sistor sections  are  dependent  upon  the  particular  application. 

Temperature. — Thermostats  are  placed  in  the  machine  bear- 
ings and  in  each  resistor  section.  Should  an  overload  persist 
to  the  extent  of  overheating  a  section  of  the  resistor,  or  should 
a  machine  bearing  reach  a  dangerous  temperature,  the  station 
will  be  shut  down  by  the  short-circuiting  of  the  coil  of  master 
relay  (3).  When  the  resistor  temperature  returns  to  normal 
the  station  comes  back  on  the  line,  unless  prevented  by  the 
setting  of  lockout  relay  (30).  However,  the  station  once  shut 
down  due  to  an  overheated  bearing  can  only  be  restored  to  serv- 
ice by  resetting  the  thermostat  contacts  by  hand. 

In  order  to  take  the  maximum  advantage  of  the  overload 
capacity  of  the  synchronous  converter,  the  current  limiting 
devices  are  usually  set  to  correspond  to  the  momentary  overload 
rating,  while  a  Replica  Thermal  Relay  protects  against  sustained 
or  repeated  overloads.  This  device  is  essentially  a  thermostat 
having  a  temperature  characteristic  similar  to  that  of  the  machine 
which  it  protects  and  is  heated  by  a  current  proportional  to 
that  in  the  converter  armature.  As  the  armature  conductors 
approach  a  dangerous  temperature,  the  thermostat  contacts  close, 
shunting  the  coil  of  master  relay  (3),  thereby  shutting  down  the 
station  until  the  apparatus  has  cooled. 

Alternating-Current  Overload. — Should  trouble  develop  be- 
tween the  high  tension  side  of  the  power  transformers  and  the 
direct-current  limiting  resistor,  protection  is  obtained  by  the 
operation  of  alternating-current  overload  relays  (23)  which 
short-circuit  the  coil  of  master  relay  (3)  thereby  shutting  down 
the  station. 

Polarity. — The  fact  that  the  polarized  motor  relay  (7)  must 
rotate  in  a  clockwise  direction,  in  order  to  establish  the  proper 


LARGE  PANEL  SWITCHBOARDS  349 

sequence  of  operations,  insures  the  machines  coming  onto  the 
line  with  correct  polarity. 

Reverse  Current.— The  equipment  includes  the  usual  direct- 
current  reverse-current  relay  (32)  which,  when  the  contacts  are 
closed,  short-circuits  the  coil  of  master  relay  (3)  thus  shutting 
down  the  station. 

Overspeed. — The  usual  speed  limit  device  (24)  mounted  on 
the  converter,  furnishes  protection  from  overspeed  by  opening 
master  relay  (3). 


_\ 

FIG.  211. — Westinghouse  automatic  substation 


Thermostat. — Liquid  thermostats  of  the  copper  bellows 
type  are  placed  in  the  machine  bearings  and  in  each  resistor 
section.  The  converter  bearings  are  so  arranged  that  the  operat- 
ing element  of  the  thermostats  is  embedded  in  the  bearing  shell. 
Thermostats  of  this  type  are  very  rugged  and  operate  very 
satisfactorily  throughout  wide  ranges  of  temperature. 

Lockout  Feature. — This  feature  is  provided  by  a  notch  up 
relay  (30)  which  operates  each  time  the  main  oil  switch  closes 
and  is  reset  to  zero  position  by  the  closing  direct-current  contac- 
tor (15).  If  the  oil  breaker  closes  three  times  before  the  direct- 
current  contactor  (15)  is  closed,  the  contacts  of  relay  (30)  close, 
short-circuiting  the  coil  of  the  master  relay  (3)  thus  locking  out 


350         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

the  station  until  the  trouble  has  been  remedied  and  relay(30) 
reset  by  hand. 

Continuous  Running. — If  the  2-pole  double-throw  switch 
(17)  is  thrown  to  the  right,  the  underload  delay  relay  (27)  is 
out  of  circuit  and  the  station  will  start  and  run  continuously 
but  with  all  automatic  protective  features.  A  typical  automatic 
substation  arrangement  is  shown  in  Fig.  211. 

PORTABLE  SUBSTATIONS 

In  connection  with  many  railway  systems  employing  synchron- 
ous converters  it  is  frequently  advisable  to  have  a  synchronous 


High  Tension  Met 


Plan  View 


DC  Outlet 


Sectional  Elevation 

FIG.  212. — Sectional  view  of  portable  substation. 

converter  with  its  transformer  and  switchboard  equipment  placed 
in  a  suitable  car  so  that  it  can  be  moved  from  one  part  of  the 
system  to  another  wherever  there  is  an  extra  demand  for  current 
that  cannot  be  taken  care  of  by  the  nearest  substation.  Owing 
to  the  low  head  room  in  a  car  and  the  necessity  for  compact 


LARGE  PANEL  SWITCHBOARDS  351 

and  simple  equipment,  the  standard  synchronous  converter  equip- 
ment has  been  modified  utilizing  small  panels  but  providing  all 
necessary  control  and  metering  equipment  except  that  for  the 
high  voltage  side  of  the  step  down  transformers. 

They  are  designed  for  300-K.W.  and  500-K.W.  25-cycle  and 
60-cycle,  6-phase  synchronous  converters,  which  are  self-starting 
from  the  alternating-current  side. 

The  panels  are  1%  inches  thick  with  %-inch  bevels,  mounted 
on  angle  iron  framework  extended  for  bracing  to  the  roof  of  the 
car. 

The  circuit  breaker,  knife  switch,  and  instrument  equipment 
for  the  low  voltage  alternating-current  and  the  direct-current  sides 
of  the  converter  is  the  same  as  previously  outlined,  except  that  the 
alternating-current  starting  knife  switch  is  hand  operated,  re- 
mote control,  for  mounting  under  the  car. 

Air-break  switches  having  low  voltage  trip  and  fuses  are  used 
for  protecting  the  step  down  transformers  and  the  converter. 
The  switch  is  operated  from  a  handle  on  the  panel  and  is  inter- 
locked electrically  with  the  direct-current  circuit  breaker  so 
that  the  latter  is  opened  when  the  former  trips.  Fig.  212  shows 
a  sectional  view  of  a  portable  substation. 

ELECTRICALLY  OPERATED  D.C.  SWITCHBOARDS 

Field  &  Exciter. — While  electrical  operation  is  fairly  common 
for  high  voltage  A.C.  boards  using  oil  circuit  breakers  it  is  not 
used  so  frequently  for  D.C.  or  low  voltage  A.C.  with  carbon 
breakers  but  there  are  some  cases  where  it  is  also  used  to  ad- 
vantage for  low  tension  A.C.  or  D.C.  service  using  carbon  cir- 
cuit breakers.  Probably  the  place  where  electrical  operation  is 
used  most  frequently  for  D.C.  service  is  for  the  control  of  ex- 
citers and  field  circuits  in  a  generating  station  where  electrical 
control  is  employed  for  the  main  A.C.  circuits  and  the  exciter  and 
field  circuits  are  electrically  controlled  from  the  generator  switch- 
board. 

Rio  de  Janeiro. — Where  the  distance  from  the  switchboard  to 
the  field  switches  and  field  rheostats  is  great,  it  frequently  be- 
comes advisable  to  operate  these  devices  electrically.  These 
are  frequently  combined  to  form  a  switchboard  like  that  shown 
in  Fig.  213  which  was  supplied  by  the  Westinghouse  Electric  and 
Manufacturing  Company  to  control  the  field  circuits  of  six  5000- 


352         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

K.V.A.  generators  and  the  field  and  armature  circuits  of  three 
200-K.W.  250-volt  exciters.  Each  exciter  is  provided  with  two 
800-ampere,  3-pole,  solenoid  operated  carbon  breakers  for  connect- 
ing to  either  or  both  of  two  sets  of  direct-current  bus  bars,  one  of 
which  is  used  for  light  and  power  service,  and  the  other  for 
excitation.  The  generator  panels  are  provided  with  2-pole,  sole- 
noid operated  field  switches  and  motor  operated  field  rheostats. 


FIG.  213. — Field  &  exciter  switchboard  for  Rio  de  Janeiro. 

Rheostats. — The  motor  operated  field  rheostat  faceplate  used 
in  this  plant  is  provided  with  a  clutch,  so  that  in  case  of  trouble 
to  the  motor  the  faceplate  may  be  operated  by  hand  after  dis- 
engaging the  clutch.  With  this  faceplate  a  signal  switch  is  pro- 
vided to  actuate  a  lamp  on  the  switchboard  when  the  arm  is 
bridging  two  contacts.  This  faceplate  is  also  provided  with  a 
limit  switch  that  opens  up  the  motor  circuit  when  the  arm  has 
reached  the  limit  of  its  travel  in  either  direction,  and  the  connec- 
tions are  so  made  that  while  the  motor  can  no  longer  be  operated 
in  one  direction  it  can  be  run  in  the  opposite  direction. 

Inawashiro. — In  certain  cases  it  is  preferable  to  mount  the 
electrically  operated  field  rheostats  entirely  independent  of  the 
field  switchboard  which  is  then  reserved  exclusively  for  the  ex- 
citer breakers  and  the  generator  field  switch  equipment  as  shown 
in  Fig.  214,  which  shows  the  exciter  and  field  switchboard  fur- 
nished by  the  Westinghouse  Company  for  the  Inawashiro  Hydro 
Electric  Company  of  Japan,  for  the  control  of  four  200-K.W.  250 
volt  exciters  and  the  field  circuits  of  the  six  7700-K.  V.  A.  generators. 


LARGE  PANEL  SWITCHBOARDS 


353 


This  switchboard  comprises  six  panels  of  marine  finished  slate 
mounted  on  a  self-supporting  pipe  framework  with  the  back  of 
the  board  completely  enclosed  by  an  open  mesh  grill  with  locked 
doors  at  each  end. 

The  two  panels  for  the  field  circuits  of  the  generators  each 
contain  six  2-pole  solenoid  operated  field  discharge  switches  used 
in  pairs  for  connecting  the  field  circuits  of  three  generators  to 
either  of  the  two  sets  of  field  bus  bars.  These  field  switches  are 
electrically  interlocked  in  pairs  in  such  a  way  that  only  one  of  a 
pair  can  be  closed  at  a  time. 


FIG.  214. — Field  &  exciter  switchboard  for  Inawashiro. 


The  four  remaining  panels  which  control  the  armature  circuits 
of  the  exciters  each  contain  two  2-pole  solenoid  operated  carbon 
break  circuit  breakers  provided  with  overload  and  reverse-current 
definite  time  limit  relays  so  arranged  that  any  exciter  can  be 
connected  to  either  of  the  two  sets  of  busses  and  the  breakers  are 
interlocked  so  that  the  exciter  can  only  be  connected  to  one  bus 
at  a  time. 

HEAVY  D.C.  ELECTRICALLY  OPERATED  BOARDS 

Aluminum  Company  of  America. — As  an  example  of  electrical 
control  applied  to  heavy  capacity  low  voltage  service,  Fig.  215 
shows  the  interior  of  the  Marysville  station  of  the  Aluminum 
Company  of  America  containing  nine  2500-K.W.  550- volt  rotary 
converters.  The  control  desk  may  be  noticed  in  the  rear  of  the 

23 


354         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

station  on  the  switchboard  gallery  and  this  contains  the  necessary 
controllers  and  meters  for  the  various  circuits. 

One  of  the  nine  synchronous  converters  is  a  spare  while  the  re- 
maining eight  are  operated  in  two  groups  of  four  each  in  parallel 
on  the  D.C.  end  and  on  the  A.C.  end  are  fed  from  four  sets  of 
secondary  leads  from  the  same  transformer  bank.  The  low  ten- 
sion A.C.  leads  are  brought  in  from  the  transformers  through  the 
right-hand  wall.  Three  of  the  six  phases  run  direct  to  the  synch- 


FIG.  215. — Marysville  station  of  Aluminum  Co.  of  America. 

ronous  convetrers  while  the  remaining  three  pass  through  the  2500 
amperes  3-pole  solenoid  operated  carbon  breaker  near  the  right 
hand-wall.  The  synchronous  converters  are  started  from  the 
D.  C.  end  and  synchronized  before  being  thrown  in  on  the  A.C. 
end.  For  starting  after  a  complete  shut  down  an  A.C.  starting 
motor  is  provided  for  starting  either  of  two  synchronous  converters 
these  in  turn  furnish  the  direct  current  for  starting  the  others. 
The  spare  rotary  can  be  operated  from  any  of  the  windings  of 
either  of  the  two  transformer  banks  in  place  of  a  rotary  that  is 
out  of  commission  and  there  is  a  spare  transformer  that  can  be 
used  in  place  of  any  of  the  six  regular  transformers. 


LARGE  PANEL  SWITCHBOARDS  355 

For  the  D.C.  end  of  each  rotary  twc  5000-ampcre  solenoid 
operated  carbon  breakers  are  furnished  and  a  20,000-ampere 
breaker  is  supplied  in  the  outgoing  feeder  fed  from  four  synch- 
ronous converters  in  parallel. 

G.  E.  Installations. — A  number  of  large  electrically  operated 
carbon  break  circuit-breaker  outfits  were  supplied  by  the  Gen- 
eral Electric  Company  for  the  substations  of  the  Interborough 
and  Metropolitan  System  in  New  York  City  and  to  other  plants 
in  different  places. 


There  are  also  numerous  installations  of  electrically  operated 
carbon  circuit  breakers  furnished  by  other  builders  for  steel  mill 
service  and  large  industrial  plants. 

I.  T.  E.-Ford  Plant. — One  of  the  most  interesting  installations 
of  I.  T  .E  .  circuit  breakers,  both  hand  and  electrically  operated 
in  a  very  large  capacity,  direct-current  installation,  is  at  the  plant 
of  the  Ford  Motor  Company,  in  Detroit,  where  there  are  fourteen 
3750-K.W.,  one  2500-K.W.  and  one  1000-K.W.  250-volt  D.C. 


356         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

generators  connecting  to  two  250-volt  D.C.  busses  and  supplying 
energy  to  a  large  number  of  D.C.  feeders. 

Main  Control  Board. — A  partial  view  of  the  main  switch- 
board showing  the  generator  control  panels  is  given  in  Fig.  216. 
The  panel  at  the  extreme  right-hand  end  contains  graphic 
instruments,  the  next  two  panels  gyrostatic  voltage  balance 
detectors,  the  next  panels  being  generator  control  panels  with 
flush  mounted  illuminated  dial  Weston  ammeters,  Sangamo 
watt-hour  meters  and  special  control  switches  used  with  the 
generator  breakers,  signals,  etc.  Then  there  are  more  panels 
with  gyrostatic  balancers,  graphic  meters,  control  circuits,  etc. 
The  other  end  of  the  switchboard  controls  D.C  feeders  with  2- 
pole  carbon  breakers  at  the  top,  round  pattern  flush  mounted 
Weston  ammeters,  and  2-pole  double-throw  knife  switches  so 
arranged  that  the  feeders  can  be  connected  to  either  of  the  two 
sets  of  bus  bars.  On  the  gallery  above  are  located  additional 
feeder  panels. 

Signals. — To  facilitate  the  operation  of  the  plant  by  the 
switchboard  attendant,  a  complete  system  of  signals  is  provided 
between  each  engine  and  the  control  section  of  the  switchboard. 
On  the  signal  board  is  mounted  an  ammeter  indicating  the 
generator  current,  two  voltmeters  showing  the  voltage  on  the 
respective  sides  of  the  3-wire  ignition  circuit,  a  switch  for 
completing  the  ignition  circuit  independent  of  the  auxiliary  switch 
associated  with  the  generator  circuit  breaker,  and  four  signalling 
switches.  With  each  switch  is  associated  a  signal  lamp  having  a 
distinctively  colored  bull's  eye  lens.  At  the  switchboard  is 
installed  an  identical  set  of  lamps  so  that  the  signal  given  by  the 
engineer  lights  the  corresponding  lamp  at  the  signal  board  as 
well  as  the  switchboard,  and  at  the  latter  point  a  bell  is  also 
rung  in  order  to  insure  the  prompt  attention  of  the  operator. 

Circuit  Breakers. — Those  controlling  the  respective  generators 
are  of  the  type  shown  in  Fig.  217,  these  being  triple-pole  double- 
throw  controlling  the  positive,  negative  and  equalizer  leads  and 
providing  alternative  connections  with  either  of  the  two  sets  of 
busses.  They  are  equipped  with  direct-acting  overload  time 
limit  features  in  each  main  lead,  and  with  reverse-current  trip  in 
the  negative  lead,  thus  insuring  the  generators  against  short 
circuit  or  unduly  sustained  overloads  and  also  against  motoring. 

Mechanism. — The  remote  control  mechanisms  are  operated  by 
means  of  motors,  there  being  one  of  these  mechanisms  for  each 


LARGE  PANEL  SWITCHBOARDS 


357 


pole.  Directly  associated  with  these  are  interlocking  devices  so 
arranged  that  the  poles  of  the  circuit  breaker  may  be  closed  only 
in  predetermined  sequence;  i.e.,  equalizer  first,  then  positive  and 
finally  the  negative  pole.  When  the  circuit  breaker  is  in  the  full 
open  position,  positive  and  negative  switch  members  of  both 
throws  are  locked  out,  and  only  the  equalizer  members  are  free 


FIG.  217. 

to  be  moved  to  the  closed  position.  Whichever  throw  of  the 
equalizer  is  closed,  the  other  is  thereupon  locked  open,  while 
the  positive  pole  which  corresponds  with  the  closed  equalizer 
pole  is  at  the  same  time  unlocked.  The  subsequent  closing  of 
this  member  unlocks  the  corresponding  negative  pole.  The 
interlocks  above  referred  to  are  mechanical  and  are  effective 
whether  the  apparatus  is  operated  electrically  or  by  hand. 

Synchronous    Converter    Starting. — Another    rather   special 
arrangement  of  motor  operated  double-throw  carbon  break  circuit 


358         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

breaker  is  shown  in  Fig.  218,  this  illustrating  the  starting  and 
running  switch  for  use  with  a  2000-K. W.  booster  converter.  This 
starting  switch  consists  of  a  3-pole,  two  step  arrangement  for  the 
purpose  of  applying  first,  low  voltage,  and  then  full  voltage  to  the 
alternating-current  end  of  the  rotary.  The  three  upper  poles 


FIG.  218. 

which  operate  as  a  unit,  carry  the  starting  current  which  is  sup- 
plied at  93  volts,  60  cycles  and  reaches  9250  amperes  as  a  maxi- 
mum. These  poles  are  amply  capable  of  rupturing  this  current 
in  the  event  of  failure  of  the  synchronous  converters  to  start. 
The  three  lower  poles  which  also  operate  as  a  unit  carry  the  run- 
ning current  which  may  attain  a  maximum  of  5500  amperes,  the 
voltage  being  193. 


LARGE  PANEL  SWITCHBOARDS  359 

Both  starting  and  running  elements  of  the  switch  are  arranged 
for  either  hand  or  remote  control  and  the  two  elements  are  so 
interlocked  both  mechanically  and  electrically  as  to  insure  proper 
sequence  of  operation  under  any  and  all  conditions.  The  con- 
struction is  such  that  it  is  impossible  to  close  the  starting  switch 
unless  the  running  switch  is  opened.  The  preliminary  movement 
of  the  running  switch  for  the  closed  position  causes  the  immediate 
opening  of  the  starting  switch  so  that  the  arc  on  this  switch  is 
broken  before  the  circuit  is  established  for  the  running  switch. 

As  further  protection  against  the  improper  application  of  full 
potential  to  the  synchronous  converters  an  induction  relay  is  pro- 
vided which  locks  the  running  switch  in  the  open  position  until  the 
rotary  is  running  at  very  near  synchronism.  This  induction  relay 
is  so  sensitive  in  its  operation  that  it  may  readily  be  adapted 
to  release  the  running  switch  only  when  the  synchronous  converters 
is  half  cycle  or  less  per  second  out  of  synchronism. 


CHAPTER  XIV 
HAND  OPERATED  A.C.  SWITCHBOARDS 

EXCITER  PANELS 

As  practically  all  A.C.  switchboards  have  to  take  care  of  the 
exciters  as  well  as  the  A.C.  generators  and  the  feeder  circuits, 
the  exciter  panels  can  really  be  considered  as  part  of  an  A.C. 
switchboard  and  are  made  to  line  up  in  general  arrangement  with 
the  A.C.  board.  The  panels  for  the  control  of  the  exciters  used 
with  alternating-current  generators  are  essentially  the  same  as 
other  2-wire  direct-current  generator  panels  except  that  no 
automatic  protection  is  provided.  Panels  are  suitable  for 
generator  voltage  regulators,  either  with  or  without  control  for 
motor  driven  exciters.  They  are  designed  to  match  and  form 
part  of  the  standard  alternating-current  switchboards. 

Limits. — The  capacity  of  a  single  exciter  circuit  is  usually 
limited  to  300  amperes  for  the  48-inch  panels  and  1600  amperes 
for  the  90-inch  panels. 

Protection. — Standard  practice  in  supplying  switchboard 
apparatus  for  control  of  exciter  circuits  is  to  furnish  non-auto- 
matic switching  devices.  Where  the  exciters  are  driven  by 
alternating-current  motors,  the  automatic  circuit  breaker  in  the 
motor  supply  will  be  furnished  with  a  high  overload  setting. 

This  practice  is  in  harmony  with  the  Rules  and  Require- 
ments of  the  National  Electrical  Code  and  is  justified  both  be- 
cause contrary  practice  would  jeopardize  the  continuity  of  the 
alternating-current  service,  and  because  modern  exciting  apparatus 
is  very  reliable. 

However,  if  special  conditions  make  it  necessary  to  provide 
automatic  protection  in  an  exciter  circuit,  the  builders  are  pre- 
pared to  supply  suitable  devices  even  though  at  variance  with 
their  usual  recommendations  and  practice. 

Field  Discharge. — It  should  be  noted  that  any  device  to  open 
a  live  field  circuit  must  be  provided  with  a  field  discharge  resist- 
ance, as  otherwise  the  opening  of  such  a  circuit  may  induce  a 
voltage  in  the  field  windings  tending  to  puncture  the  insulation. 


HAND  OPERATED  A.C.  SWITCHBOARDS 


361 


In  some  cases  with  parallel-operated  exciters  it  may  be  desir- 
able to  provide  automatic  devices  that  operate  only  on  reversal  of 
energy  in  an  exciter  circuit,  in  order  to  disconnect  a  defective 
exciter.  In  such  cases  standard  generator  panels  having  auto- 
matic circuit  breakers  may  be  used  by  omitting  the  overload 
feature  on  the  breakers  and  adding  the  necessary  reverse-current 
devices. 

Connections. — Fig.  219  shows  typical  connections  for  a  steam 
driven  exciter,  a  motor  operated  exciter,  a  voltage  regulator  and 


Fio.  219. — Typical  connection  exciter  and  field  connections. 

the  field  circuits  of  two  generators.  The  usual  equipment  for 
an  exciter  comprises  a  3-pole  switch  or  a  2-pole  main  switch 
and  a  single-pole  equalizer  switch  with  an  ammeter,  a  voltmeter 
switch  and  a  field  rheostat  for  the  main  exciter  circuit  as  well  as 
one  for  use  with  the  exciter  voltage  regulator.  One  voltmeter 
takes  care  of  two  or  more  exciters. 


A.C.  SWITCHBOARDS  WITH  KNIFE  SWITCHES 

For  moderate  voltage  installations  in  industrial  plants  and 
small  central  and  distributing  stations  where  voltages  do  not 
exceed  480  volts,  panels  with  knife  switches  and  enclosed  fuses 
can  be  used  where  the  cost  of  a  switchboard  with  oil  circuit 


362         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

breakers  is  not  justified.  Enclosed  fuses  must  not  be  supplied 
under  conditions  where  the  available  current  on  short  circuits 
exceeds  the  limits  fixed  by  the  National  Electrical  Code. 

Limits. — The  capacity  of  a  single  generator  panel  is  usually 
limited  to  1000  amperes,  a  single  feeder  circuit  to  600  amperes, 
and  a  complete  switchboard  composed  of  these  panels  to  2000 
amperes  in  any  section  of  the  bus  bars.  Where  the  total  capa- 
city exceeds  2000  amperes  the  panels  should  be  arranged  with  the 
feeders  and  generators  interleaved  in  such  a  way  that  no  part 
of  the  bus  will  have  to  carry  more  than  2000  amperes. 

Voltage  Readings. — With  the  apparatus  supplied  on  the  gen- 
erator panels  and  with  the  bus  instrument  equipments,  provision 
is  made  for  the  indication  of  voltage  on  one  phase  of  the  bus  and 
on  any  phase  of  the  machine.  Provision  can  be  made  for  indica- 
tion of  voltage  on  any  phase  of  the  bus  and  on  one  phase  of  the 
machine.  Synchronizing  is  done  between  bus  and  machine  by 
means  of  a  synchronoscope. 

If  a  sectionalized  bus  is  used,  a  voltmeter  switch  is  needed  to 
transfer  the  bus  voltmeter  to  either  section  of  the  bus.  The  bus 
instrument  equipments  include  lamps  for  mounting  on  the 
panels  for  continuous  ground  indication. 

Generator  panels  include  drilling  for  remote-control  rheostat 
mechanism,  but  the  mechanism  is  not  included  as  part  of  the 
switchboard.  No  automatic  overload  protection  for  the  gen- 
erator armature  or  field  circuits  is  supplied.  Enclosed  fuses 
provide  automatic  overload  protection  for  the  feeder  circuits. 

Switches. — Round  stud  knife  switches  without  quick  break 
attachments  are  furnished  with  standard  panels.  When  cir- 
cuits must  be  frequently  opened  under  load,  quick  break  switches 
are  recommended  for  100  amperes  and  above. 

Blank  Panels. — It  is  desirable  to  install  blank  panels  in  cases 
where  the  future  equipment  cannot  be  placed  at  either  end  of 
the  board.  Such  provision  at  the  time  of  the  original  installa- 
tion makes  it  unnecessary  to  move  existing  panels  and  connecting 
conductors  at  the  time  of  making  additions. 

Panels  with  single-throw  switches,  for  operating  with  a  single 
bus  system  only,  are  usual.  Panels  with  double-throw  switches 
for  operating  with  a  double-bus  system  can  be  supplied.  Ordi- 
narily, for  plants  of  moderate  capacity  the  sectionalizing  of  the 
lighting  load  and  the  power  load  may  be  obtained  by  grouping 
all  the  lighting  circuits  on  one  section  of  the  bus  and  the  power 


HAND  OPERATED  A.C.  SWITCHBOARDS  363 

circuits  on  the  other  section,  the  two  sections  being  connected 
together,  when  desired,  by  a  switch.  This  permits  carrying  all 
the  load  with  one  machine  during  light-load  periods. 

A.C.  SWITCHBOARDS  WITH  OIL  CIRCUIT  BREAKERS 

For  higher  voltages  and  in  many  cases  for  moderate  voltages 
it  is  advisable  to  utilize  oil  circuit  breakers  and  these  may  be 
mounted  directly  on  the  rear  of  the  switchboard  or  made  distant 
control  operated  mechanically  or  electrically  depending  on 
various  circumstances.  The  general  appearance  of  the  A.C. 
panel  switchboards  is  largely  influenced  by  the  type  of  instru- 
ments used  and  by  the  cover  plate  or  control  device  employed 
with  the  oil  circuit  breakers. 

These  switchboards  are  designed  to  control  the  alternating- 
current  electrical  equipment  of  central  and  distributing  stations 
and  industrial  plants. 

Direct-control. — These  boards  are  designed  for  plants  not 
exceeding  3000-kilovolt-amperes  capacity,  requiring  panels  not 
exceeding  800  amperes  capacity,  where  the  voltage  is  not  over 
2400  and  where  it  is  not  so  advantageous  to  locate  the  oil  switch- 
ing devices  apart  from  the  panels. 

Hand  Remote  Control. — These  switchboards  are  applicable 
where  the  simplicity  of  connections  or  accessibility  desired  cannot 
be  obtained  with  panel  mounted  apparatus,  where  station  capa- 
city of  voltage  is  so  high  as  to  make  it  desirable  to  mount  switch- 
ing equipment  apart  from  panels,  and  where  station  arrangement 
permits  the  use  of  manually  operated  remote  control  oil  circuit 
breakers. 

Electrical  Remote  Control. — These  switchboards  are  applicable 
where  the  equipment  must  be  remote  controlled  but  where 
manually  operated  switchboard  apparatus  is  not  suitable. 

Accessibility. — To  make  the  rear  of  the  switchboard  more 
accessible,  all  the  current  transformers  are  usually  furnished  for 
mounting  apart  from  the  panels,  and  arrangements  should  be 
made  for  mounting  these  transformers  in  the  main  leads  in  the 
most  suitable  location.  Voltage  transformers  will  usually  be 
mounted  on  the  rear  of  panels,  as  this  location  is  advisable  in 
order  to  get  the  advantage  of  short  primary  leads  and  ready 
access  to  primary  fuses.  This  applies  chiefly  to  direct-control 
switchboards. 


364         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


Panel  Frame  Mounting. — Additional  advantages  in  construc- 
tion can  often  be  obtained  by  the  use  of  breakers  mounted  on 
panel  framework.  Usually  oil  circuit  breakers,  both  non-auto- 
matic and  automatic,  can  be  supplied  for  mounting  on  horizontal 
pipes  attached  to  the  panel  framework  back  of  the  operating 
handle,  as  shown  in  Fig.  220.  In  general,  the  panel  frame  mount- 
ing gives  a  better  construction,  in  that  connections  from  circuit- 
breakers  to  bus  bars  are  more  nearly 

C  c  3Li=s=s==s=ss=s=si  |  direct  and  more  space  is  available  for 
taking  away  connecting  cables  to 
panels  and  for  mounting  switchboard 
details.  Some  of  the  other  advantages 
are  the  following:  less  likelihood  of 
oil  getting  on  panels;  the  weight  of 
breakers  is  carried  on  frame  instead 
of  on  panel;  the  rear  of  the  panels  is 
more  accessible;  several  types  and 
capacities  of  breakers  have  inter- 
changeable mountings;  with  narrow 
panels  the  position  of  the  breaker 
handle  is  not  restricted  to  the  center 
of  the  panel  so  that  knife  switches 
and  handles  for  remote  control  breakers  can  often  be  added 
where  this  would  be  impossible  with  direct  panel  mounting 
unless  wider  panels  are  used. 

Voltage  Readings. — With  apparatus  supplied  on  the  generator 
panels  and  with  the  usual  bus  instrument  equipments,  provision 
is  made  for  reading  the  voltage  on  one  phase  of  the  bus  and  on  any 
phase  of  the  machine  for  240,  480,  and  600-volt  systems,  when 
voltmeters  are  wound  for  primary  voltage;  and  for  reading  the 
voltage  on  any  phase  of  the  bus  and  on  one  phase  of  the  machine 
on  systems  of  higher  voltage,  or  in  cases  where  voltmeters  are 
wound  for  secondary  voltage  on  systems  of  600  volts  and  under. 
Synchronizing  is  done  between  bus  and  machine  by  means  of  a 
synchronoscope. 

If  the  voltage  indication  on  all  three  phases  on  the  machine 
side  of  the  generator  circuit  breaker  is  desired  for  panels  having 
secondary  voltage  instruments,  it  is  necessary  to  supply  with 
each  generator  panel  a  3-phase  voltmeter  switch,  and  an  addi- 
tional voltage  transformer. 
Meter  Equipment. — Direct-control  switchboard  equipments 


FIG.  .  220. — Switchboard    with 
panel  frame  mounted  breakers. 


HAND  OPERATED  A.C.  SWITCHBOARDS 


365 


include  power  factor  meters,  wattmeters,  and  watt-hour  meters 
with  windings  for  bus  voltage  for  240  and  480  volts,  and  volt- 
meters and  frequency  meters  with  coils  for  bus  voltages  for  240, 
480  and  600  volts.  For  bus  voltages  above  these  values,  voltage 
transformers  are  required.  Synchronoscopes  require  voltage 
transformers  for  all  voltages  above  115  (nominal). 


FIG.  221. — Typical  low  voltage  Westinghouse  switchboard. 

The  question  of  the  arrangement  of  circuit  breakers  and  bus 
bars  will  be  considered  later  and  a  few  typical  examples  of  General 
Electric  and  Westinghouse  panel  boards  will  be  given  to  illus- 
trate the  principal  features  of  design. 

Westinghouse  Switchboards. — Fig.  221  shows  a  typical  low 
voltage  A.C.  Westinghouse  switchboard  for  the  control  of  two 
exciters,  one  exciter  motor,  two  generators  and  two  feeders. 
On  swinging  brackets  are  placed  two  voltmeters,  one  connected 
to  the  bus  and  the  other  plugging  on  any  generator,  and  a 
synchronoscope  with  two  synchronizing  lamps. 


366         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

The  double  exciter  panel  contains  two  2-pole  exciter  main 
switches,  one  single-pole  equalizer  switch,  two  exciter  ammeters 
with  one  voltmeter  and  voltmeter  switches  for  connecting  it  to 
either  exciter.  The  next  panel  for  the  exciter  motor  contains 
the  handle  for  the  auto  starter  and  an  ammeter. 

Each  generator  panel  contains  an  A.C.  ammeter  with  three- 
way  switch  to  connect  it  to  any  phase,  a  polyphase  indicating 
wattmeter,  a  field  ammeter,  voltmeter  and  synchronizing 
switches,  field  rheostat  and  field  discharge  switch  with  resistor 
and  main  3-pole  knife  switch. 


FIG.  222. — Panel  switchboard,  hand  operated  breakers — General  Electric  Co. 


G.  E.  Panel  Board. — Figure  222  shows  a  typical  General  Elec- 
tric switchboard  supplied  to  the  Catton,  Neill  &  Co.,  Ltd.,  of 
Honolulu,  H.  I.  This  board  controls  two  exciters,  one  480  volt 
3  phase  3  wire  A.C.  generator,  one  480  volt  3  phase  3  wire  incom- 
ing line,  six  480  volt  3  phase  3  wire  power  feeders  and  various 
lighting  feeders.  The  synchronoscope,  exciter  voltmeter,  etc., 
are  mounted  on  swinging  panel  adjoining  exciter  panel.  The 
three  phase  generator  panel  is  provided  with  horizontal  edgewise 
A.C.  ammeter,  voltmeter,  indicating  wattmeter  and  field  am- 
meter, field  rheostat,  field  switch  with  discharge  clips,  voltmeter 
and  synchronizing  receptacles,  non-automatic  generator  main 
switch,  watthour  meter  and  testing  receptacles.  The  next  panel 
is  the  incoming  line  panel  and  is  provided  with  indicating  meters, 
voltmeter  and  synchronizing  receptacles,  ammeter  plug  recep- 
tacles, plunger  type  overload  relays,  automatic  oil  circuit  breaker, 


HAND  OPERATED  A.C.  SWITCHBOARDS 


367 


watthour  meter  and  calibrating  receptacles.  The  next  four 
panels  are  power  feeder  panels  controlling  a  total  of  six  circuits 
and  each  circuit  is  provided  with  the  following: 

Ammeter 

Ammeter  plug  receptacles 

Ammeter  plunger  type  overload  relays  and  automatic  oil 
circuit  breaker. 

The  panels  at  extreme  right  hand  end  of  switchboard  control 
various  lighting  circuits,  each  circuit  provided  with  a  3  pole 
knife  switch  properly  fused. 


FIG.  223. — Electrically  operated  switchboard  round  meters. 

Electric  Operated  Switchboard.— Fig.  223  shows  a  typical 
panel  switchboard  using  7-inch  diameter  black  dial  round  pattern 
instruments  with  distant  electrical  control  oil  circuit  breakers. 
The  swinging  bracket  contains  the  bus  voltmeter,  the  machine 
voltmeter,  the  exciter  voltmeter  and  the  synchronoscope  with 
two  synchronizing  lamps.  The  first  panel  on  the  left  contains 
the  voltage  regulator  for  three  exciters  not  operating  in  parallel 
and  contains  the  various  relays,  rheostats,  switches,  etc.,  needed 
for  the  regulating  equipment.  Each  of  the  next  three  panels 


368         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

controls  a  generator  with  its  direct  connected  exciter.  Each 
panel  is  provided  with  an  ammeter  with  three  way  ammeter 
switch,  a  polyphase  indicating  wattmeter,  a  field  ammeter,  an 
exciter  rheostat,  field  switch  with  discharge  resistor,  a  volt- 
meter and  synchronizing  receptacle,  a  control  switch  for  the 
motor  operated  generator  rheostat,  a  control  switch  for  the  gover- 
nor motor,  a  control  switch  with  indicating  lamps  for  use  with 
the  electrically  operated  breaker  in  the  generator  circuit,  two 
single-phase  overload  relays  and  a  watthour  meter.  The  re- 
maining panels  are  feeder  panels,  one  of  them  containing  a 
graphic  wattmeter. 


FIG.  224. — G.E.  truck  type  switchboard  front  view. 

Truck  Type. — One  of  the  latest  developments  in  the  way  of 
A.C.  panel  switchboards  is  the  truck  type  of  design  shown  in 
Fig.  224  in  front  view  with  one  of  the  trucks  withdrawn,  and  in 
side  view  Fig.  225.  This  type  of  switchboard  is  made  up  of  re- 
movable truck  type  panels  and  can  be  supplied  in  separate  units 
or  built  up  to  form  a  complete  switchboard  with  its  accessories. 
Connections  are  automatically  broken  as  soon  as  the  truck  is  re- 
moved from  the  compartment,  positively  insuring  that  workmen 
have  no  live  parts  to  handle.  One  great  advantage  is  obtained  in 
that  continuity  of  service  is  assured.  Should  a  breakdown  occur, 
a  spare  unit  can  immediately  be  placed  in  service  without  taking 


HAND  OPERATED  A.C.  SWITCHBOARDS 


369 


the  power  off  the  main  bus  thereby  interrupting  the  service  on 
other  sections  of  switchboard.  This  gives  great  flexibility  to  the 
station. 

Limits. — These  panels  can  be  supplied  for  voltages  up  to  7500 
and  current-carrying  capacity  up  to  800  amperes;  also  in  various 
combinations  of  oil  circuit  breaker,  instrument  transformers  and 
meters. 


FIG.  225. — G.E.  truck  type  switchboard,  side  view. 

Construction. — The  general  construction  of  the  complete  panel 
is  shown.  All  H.  T.  bus  bars  and  cable  connections  are  carried  on 
substantial  porcelain  insulators  mounted  in  the  frame  supports 
which  are  built  up  to  form  a  complete  cell  structure.  The  frame- 
work is  so  designed  that  a  new  panel  can  be  added  at  any  time, 
the  complete  structure  being  finished  off  by  cover  plates  bolted 
to  the  ends  of  the  bus  bar  chamber,  except  in  cases  where  cables 
are  to  be  connected  direct  to  the  bus  bars.  In  such  cases  a 
cable  box  can  be  fitted  to  the  opening  at  the  end  of  the  bus  bar 
chamber.  Horizontal  partitions  are  fitted  above  and  below  the 


370         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

bus  bars  so  that  the  latter  are  enclosed  in  a  separate  and  con- 
tinuous chamber.  Where  space  is  available  behind  the  panel, 
access  can  be  obtained  to  these  chambers  by  removing  the  back 
and  top  covers.  Where  space  is  limited,  however,  the  complete 
cell  structure  can  be  built  against  the  wall,  access  to  the  back 
being  obtained  through  the  hand  holes  provided. 

Covers. — Protecting  covers  for  cables  and  bus  bar  terminals 
can  be  supplied,  so  that  when  it  is  necessary  for  work  to  be 
done  in  a  cell,  while  the  terminals  are  alive,  these  covers  can  be 
padlocked  in  position  and  the  work  can  be  done  with  perfect 
safety.  Portable  cell  doors  can  also  be  supplied  for  closing  any 
cell  from  which  the  truck  has  been  removed. 

Mounting. — The  whole  of  the  apparatus  for  each  circuit 
equipment,  including  the  oil  circuit  breaker,  instruments  and 
transformers  is  mounted  on  a  movable  truck.  This  truck  can  bo 
withdrawn  in  the  space  allocated  to  the  attendant,  and  then 
wheeled  away  for  inspection.  The  open  construction  of  the 
truck  framework  renders  inspection  of  all  the  apparatus  a  very 
easy  matter. 

Contact  Jaws. — The  truck  carries  contact  jaws  mounted  on 
porcelain  insulators  which  engage  with  contact  blades  mounted 
in  the  fixed  portion  of  the  structure.  These  contact  blades  are 
sunk  into  the  porcelain  insulators  so  as  to  obviate  danger  of  acci- 
dental shock  or  short  circuits  when  the  truck  is  removed.  The 
same  insulators  also  support  the  bus  bars  in  the  bus  bar  chamber 
and  the  cable  terminals  in  the  cable  box  chamber. 

Interlocks. — Safety  interlocks  are  fitted  to  all  trucks,  so 
that  it  is  impossible  for  any  truck  to  be  withdrawn  from  the 
cell  while  the  oil  circuit  breaker  is  closed;  similarly  the  truck 
cannot  be  pushed  into  the  cell  unless  the  oil  circuit  breaker  is 
open. 

All  parts  are  held  together  by  means  of  bolt  and  lock  nuts,  so 
that  any  part  can  be  readily  removed  and  replaced  in  a  sound 
mechanical  manner. 

The  small  wiring  between  the  current  transformers,  trip  coils, 
and  instruments  is  permanently  connected  up  and  mounted  on 
porcelain  insulators  attached  to  the  frame  of  the  truck. 

The  whole  equipment  is  arranged  so  that  ample  clearances 
are  allowed  between  the  conductors,  and  from  conductors  to 
ground. 


HAND  OPERATED  A.C.  SWITCHBOARDS 


371 


ELECTRICALLY  OPERATED  EQUIPMENTS 
Arrangements. — Various  standard  arrangements  for  electric- 
ally controlled  equipments  are  shown  in  Fig.  226.  'A'  illus- 
trates a  typical  vertical  panel  board  with  the  instruments,  con- 
trol switches,  relays,  and  similar  devices  mounted  on  the  face 
of  the  panel.  'B'  shows  an  arrangement  of  a  control  desk  with 
the  control  switches  placed  on  the  desk  and  the  instruments 
mounted  on  a  wall  in  front  of  the  operator.  'C'  shows  an 
arrangement  of  control  desk  where  there  are  only  a  comparatively 
few  meters,  these  being  set  flush  in  the  face  of  the  desk.  '  D ' 
shows  a  modification  of  the  desk  arrangement  with  the  meters 
on  a  small  slab  or  bracket  extending  up  from  the  horizontal  slab 


n 


d 


n 


FIG.  226. — Arrangement  of  electrically  operated  boards. 

of  the  desk.  '  E '  shows  the  control  desk  arrangement  with  verti- 
cal panels  forming  the  back  of  the  desk,  the  vertical  panels 
containing  the  indicating  meters.  'F'  is  a  further  modifica- 
tion of  the  control  desk  arrangement  with  vertical  panels  con- 
taining the  indicating  meters  and  a  complete  switchboard  at 
the  rear  to  contain  the  recording  meters,  relays,  and  similar 
devices.  With  this  arrangement  a  self-supporting  control  desk 
is  provided.  '  G '  shows  the  so-called  gallery  type  of  desk  with 
the  meters  located  on  a  framework  supported  above  the  hori- 
zontal slab  of  the  desk  at  such  a  height  that  the  operators 
standing  at  the  control  desk  can  look  above  the  edge  of  the  desk 
and  below  the  meter  panels  to  observe  from  the  switchboard 
gallery  the  machine  which  he  is  controlling.  '  H '  is  a  modifica- 
ation  of  the  gallery  type  of  control  desk.  '!'  is  a  modified 
arrangement  of  control  desk  using  a  separate  instrument  frame 
supported  on  ornamental  pillars,  these  pillars  as  a  rule,  being 
arranged  to  form  the  supports  of  a  gallery  railing.  'J'  shows 


372         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

the  combination  of  utilizing  a  gallery  type  control  desk  for  the 
generators  and  vertical  panel  switchboard  for  the  feeders.  '  K ' 
shows  a  combination  control  desk  and  panel  board,  the  gen- 
erator breakers  being  controlled  from  the  desk,  the  generator 
instruments  being  on  the  vertical  panels  and  all  of  the  feeders 
being  controlled  from  the  vertical  panels.  The  recording  meters, 
graphic  meters,  and  relays  are  placed  on  an  auxiliary  board 
back  to  back  with  the  feeder  board.  *L'  shows  an  arrangement 
of  control  pedestals  and  instrument  posts. 

Pedestals. — In  some  of  the  earlier  large  capacity  power  plants 
equipments  of  control  pedestals  and  instrument  posts  were 
utilized  in  place  of  vertical  panels  in  conditions  where  present 
day  practice  would  probably  select  the  control  desk  as  being 
the  most  suitable  arrangement.  Some  of  these  earlier  equip- 
ments of  pedestals  and  posts  have  been  superseded  by  more 
recent  control  desks  but  others  are  still  in  operation. 

Where  the  number  of  generators  was  comparatively  small  in 
comparison  with  the  number  of  feeder  circuits,  it  was  considered 
frequently  of  advantage  to  use  control  pedestals  and  instrument 
posts  for  the  generator  circuits  and  to  take  care  of  the  feeder 
circuits  by  means  of  a  panel  switchboard.  The  instrument  posts 
and  control  pedestals  were  self-contained,  and  additional  posts 
and  pedestals  could  readily  be  added  with  additional  machines, 
without  disturbing  the  symmetry  of  the  arrangement. 

Union  E.  L.  &  P.  Co. — The  original  installation  of  pedestals 
and  posts  in  the  switching  galleries  of  the  Union  Electric  Light 
&  Power  Company  of  St.  Louis  is  shown  in  Fig.  227,  this  equip- 
ment having  been  furnished  for  the  control  of  eleven  6600- volt,  25- 
cycle,  3-phase  generators  of  various  capacities  and  a  large 
number  of  feeders.  The  generator  controlling  devices  were 
located  on  the  pedestals,  while  the  generator  instruments  were 
placed  on  posts,  the  posts  acting  as  supports  for  the  gallery 
railing.  A  station  post  containing  voltmeters,  synchronoscopes, 
etc.,  was  so  located  that  the  instruments  could  be  observed  from 
any  portion  of  the  gallery.  With  the  arrangement  shown  the 
operator  on  the  switchboard  gallery  at  the  end  of  the  station 
faced  the  generator  room,  while  standing  at  the  control  pedestals 
and  watching  the  generator  instruments.  The  feeders  were 
controlled  from  the  panel  board  back  of  the  operator,  while  the 
masonry  structure  for  the  bus  bars  and  connections  was  back  of 
the  feeder  board  and  located  on  the  control  gallery,  as  well  as 


HAND  OPERATED  A.C.  SWITCHBOARDS  373 

several  lower  galleries.  Since  the  time  of  the  original  installation, 
the  switchboard  gallery  was  enclosed  in  glass,  and  the  generator 
instruments  were  taken  off  the  instrument  posts,  and  placed  on 
swinging  panels  attached  to  the  framework  of  the  glass  enclosure. 
A  later  arrangement,  due  to  remodeling  of  the  plant  makes  use 
of  a  control  desk  equipment. 


FIG.  227. — Pedestals  and  posts  of  Union  Electric  L.  &  P.  Co.  of  St.  Louis. 

Generator  Pedestals. — Each  generator  pedestal  was  provided 
with  a  controller  for  an  electrically  operated  field  discharge 
switch,  a  drum  controller  (or  a  motor  operated  field  rheostat,  a 
drum  controller  for  the  engine  governor,  three  oil  circuit-breaker 
controllers  with  electro-mechanical  tell  tale  devices  and  a 
4-point  voltmeter  receptacle.  At  the  top  of  the  pedestal  were 
placed  synchronizing  and  signal  lamps,  while  the  synchronizing 
receptacles  and  plugs  were  located  on  each  side  of  the  lower 
circuit-breaker  controllers.  Each  pedestal  had  a  height  of  4 
feet  8^4  inches  and  occupied  a  floor  space  14  inches  square. 

Generator  Posts. — Each  generator  instrument  post  was  equip- 
ped with  a  direct-current  field  ammeter,  a  3-phase  power  factor 
indicator  and  three  A.C.  ammeters.  These  posts  were  provided 
with  railing  sockets  and  formed  the  supporting  posts  for  the 
railing  at  the  edge  of  the  switchboard  gallery.  These  instru- 
ment posts  were  made  to  contain  various  combinations  of  instru- 
ments, and  had  a  standard  height  of  5  feet  7K  inches  to  the  bot- 


374         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

torn  of  the  lowest  meter,  the  total  height  to  the  top  of  grill  work 
above  the  upper  meter  being  about  8  feet  10  inches. 

The  Ontario  Power  Co.  Control  Room,  at  Niagara  Falls,  Ont., 
is  shown  in  Fig.  228.  At  the  time  this  photograph  was  taken  the 
plant  contained  seven  8770-K.V.A.  12,000-volt,  3-phase  gen- 
erators, with  banks  of  three  3000-K.V.A.  transformers  stepping 
up  to  60,000  volts.  The  60,000-volt  feeder  circuits  running  to 
Rochester,  Syracuse,  etc.,  were  controlled  from  the  panel  board, 
while  the  two  smaller  pedestals  placed  near  the  telephone  desk 
were  used  for  the  control  of  the  exciter  circuits.  Various  changes 


FIG.  228. — Control  pedestals  &  posts  of  Ontario  Power  Co. 

have  been  made  due  to  modifications  in  the  excitation  system  and 
plant  at  present  comprises  sixteen  units  and  most  of  the  energy  is 
now  delivered  to  the  Hydro  Electric  Power  Commission  of 
Ontario. 

Control  Pedestals. — Each  of  the  seven  control  pedestals  was 
equipped  with  push-button  control  for  the  generator  field  rheo- 
stats and  with  a  white  signal  lamp,  that  lit  up  when  the  field 
circuit  was  closed.  The  miniature  bus  placed  on  the  face  of  the 
control  pedestal  shows  two  electrically  operated  oil  circuit 
breakers  in  the  main  generator  circuit,  one  placed  in  the  power 
house  at  the  foot  of  the  cliff  and  the  other  being  placed  in  the  dis- 
tributing station.  The  circuits  from  the  generator  after  passing 
through  these  two  breakers  connected  by  the  breaker  controlled 
from  the  lower  left-hand  controller  to  one  12,000-volt  bus  in  the 
distributing  station,  or  passed  through  the  breaker  controlled 
by  the  middle  controller  to  a  common  connection,  where  it 
branched  and  passed  either  through  another  breaker  to  a  second 


HAND  OPERATED  A.C.  SWITCHBOARDS  375 

12,000-volt  bus,  or  through  a  breaker  on  the  low  tension  side  of 
the  step  up  transformers.  The  controller  in  the  extreme  upper 
right-hand  corner  took  care  of  the  breaker  in  the  high  tension  side 
of  the  step  up  transformers.  The  two  remaining  controllers 
with  circular  handles  were  used,  one  for  the  control  of  the  field 
rheostat  and  the  other  for  the  control  of  the  speed  governor  motor. 
Suitable  synchronizing  lamps  and  receptacles  were  also  placed 
on  these  pedestals.  This  type  of  pedestal  is  5  feet  0  inches  high 
and  occupies  a  floor  space  approximately  24  inches  by  14  inches. 

Instrument  Post. — Each  post  was  provided  with  a  single  phase 
synchronoscope,  a  frequency  meter,  a  3-phase  power  factor 
indicator  and  transformer  and  generator  ammeters  and  similar 
instruments.  The  base  of  the  instrument  post  contained  a 
number  of  calibrating  jacks  to  permit  the  calibrating  of  the 
instruments  without  removing  them  from  the  posts.  The  total 
height  of  this  post  was  9  feet  0  inches  and  the  width  occupied  by  the 
meters  was  2  feet  7%  inches. 

Control  Desk. — The  control  desk  has  many  advantages  where 
a  very  compact  arrangement  is  desired  to  control  the  generators 
and  feeders  from  the  same  switchboard,  particularly  where  a 
group  system  of  circuits  is  used  and  it  is  desirable  to  have  a 
miniature  bus  bar  to  show  the  general  scheme  of  connections  and 
the  arrangement  of  circuits  in  use.  The  desk  has  mounted 
on  it  the  various  controllers  for  the  circuit  breakers,  field  switches, 
field  rheostats,  etc.  It  is  customary  to  mount  the  instruments 
in  such  a  position  relative  to  the  sections  of  the  desk,  as  to  indicate 
clearly  to  the  station  operator  the  instruments  belonging  to  any 
particular  circuit. 

With  control  desks  the  instruments  can  be  mounted  either 
on  independent  switchboards  or  panels  forming  the  back  of  the 
control  desk,  or  on  an  instrument  frame  back  of  and  usually 
higher  than  the  top  of  the  control  desk,  or  on  instrument  posts. 
In  some  cases  the  instrument  can  be  set  directly  in  the  face  of  the 
desk. 

Fig.  229  shows  the  front  elevation  drawing  of  the  control 
desk  supplied  to  the  Williamsburg  Generating  Station  of  the 
Brooklyn  Rapid  Transit  Company  for  the  control  of  a  number 
of  7500-K.V.A.  and  10,000-K.V.A.  turbogenerators,  the  desk 
as  shown  being  intended  for  the  control  of  nine  machines. 

Generator  Equipment. — Each  generator  is  provided  with  two 
electrically  operated  oil  breakers  in  series  with  suitable  discon- 


376         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

necting  switches  so  that  each  generator  can  connect  to  its  own 
feeder  group  bus  or  to  the  main  bus.  This  main  bus  is  sec- 
tioned by  means  of  electrically  operated  oil  breakers  between 
generators  3  and  4,  generators  5  and  6  and  generators  7  and  8. 
Group  breakers  are  also  provided  for  connecting  the  feeder  group 
busses  to  the  main  bus.  Each  feeder  group  bus  supplied  from 


1 


FIG.  229. — Front  elevation  desk,  Brooklyn  rapid  transit. 


three  to  six  feeder  breakers.  The  generator  instruments  are 
placed  on  a  framework  above  the  desk,  so  arranged  that  the 
station  operator  can  readily  watch  the  machines  which  he  is 
controlling.  Each  generator  section  is  provided  with  a  field 
ammeter,  an  A.C.  ammeter,  a  polyphase  indicating  wattmeter 
and  a  power  factor  meter,  while  a  voltmeter  was  set  in  the  top  of 
the  desk  for  one  generator  section  in  each  group.  A  synchrono- 
scope,  frequency  indicator  and  voltmeter  were  placed  on  a  pivoted 
slab  attached  to  the  center-post  of  the  instrument  frame  back  of 
the  desk. 


HAND  OPERATED  A.C.  SWITCHBOARDS 


377 


A  sectional  view  is  shown  in  Fig.  230  of  this  same  control  desk 
which  indicates  the  relative  location  of  the  desk  and  instrument 
board,  as  well  as  the  location  of  the  apparatus  on  the  face  of  the 
control  desk  with  the  relays  and  similar  devices  on  the  back  of  the 
desk. 


FIG.  230. — Side  elevation  desk,  Brooklyn  rapid  transit. 


Feeder  Board. — The  feeders  in  this  installation  are  controlled 
from  a  vertical  steel  switchboard  arranged  in  the  form  of  an  arc  of 
a  circle  back  of  the  control  desk,  so  that  the  station  operator 
turning  around  from  the  generator  desk  can  readily  observe  any 
of  the  feeder  circuits.  This  feeder  switchboard  is  made  of  two 
concentric  boards  placed  back  to  back,  the  board  on  the  concave 
side  next  to  the  generator  desk  containing  the  feeder  indicating 
instruments  of  the  vertical  edgewise  type,  and  the  controllers 
and  indicating  lamps  used  with  the  electrically  operated  breakers 
of  the  feeder  circuits,  while  the  switchboard  on  the  convex 
side  contains  the  polyphase  watt-hour  meters,  the  overload 
relays  and  the  calibrating  switches  supplied  for  the  various 
feeder  circuits. 


378         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Desk  with  Horizontal  Edgewise  Meters. — Fig.  231  shows  a 
control  desk  with  horizontal  edgewise  meters  placed  on  slate 
slabs  above  the  desk,  while  the  various  control  switches  with  their 
indicating  lamps  are  mounted  on  the  slate  apron  of  the  desk  and 
the  time  limit  relays  are  located  on  the  front  panels  of  the  desk. 
With  the  arrangement  shown  the  station  operator  faces  the 
generator  room  when  standing  at  the  desk  and  looks  over  the 
desk  and  under  the  frame  to  watch  the  machines. 


FIG.  231. — Control  desk.  G 


Electric  Co. 


Desk  with  Vertical  Edgewise  Meters. — A  control  desk  with 
vertical  edgewise  meters  supplied  to  the  Pratt  Street  Power  House 
of  the  United  Railway  &  Electric  Company  of  Baltimore  is 
shown  in  Fig.  232,  controlling  a  number  of  13200-volt,  25-cycle, 
3-phase,  generators  and  outgoing  feeder  circuits.  This  desk 
was  arranged  to  form  an  arc  of  a  circle  and  was  ultimately  to  be 
about  twice  as  large  as  the  portion  shown.  A  complete  minia- 
ture bus  bar  system  located  on  the  top  of  the  desk  shows  the 
connections  made  by  the  various  breakers  that  were  arranged 
on  a  group  and  ring  system.  In  this  plant  each  generator  was 


HAND  OPERATED  A.C.  SWITCHBOARDS  379 

provided  with  a  circuit  breaker  connecting  the  generator  to  its 
own  bus  bar.  This  bus  bar  connected  in  turn  through  a  main 
breaker  to  the  main  bus  or  through  either  of  the  two  group 
breakers  to  two  group  busses,  each  group  bus  supplying  the  cur- 
rent to  four  feeder  circuits.  By  closing  the  various  group 
breakers,  the  group  busses  form  one  complete  ring  bus  and  the 
main  bus  forms  the  second  ring  bus,  so  that  a  very  flexible  arrange- 
ment was  secured. 

Calibrating  jacks  were  installed  on  the  front  panels  of  the  con- 
trol desks  to  permit  any  of  the  switchboard  instruments  to  be 


FIG.  232. — Control  desk  with  vertical  edgewise  meters. 

calibrated  in  position.  The  vertical  edgewise  instruments  were 
mounted  on  steel  plates  forming  the  instrument  frame,  while  the 
relays  were  located  on  the  rear  of  the  desk. 

Desk  with  Round  Pattern  Meters. — Fig.  233  shows  a  control 
desk  of  the  gallery  type  furnished  by  the  Westinghouse  Electric 
&  Manufacturing  Company  to  the  Inawashiro  Hydro  Electric 
Company  of  Japan  for  the  control  of  four  exciters,  six  7700-K.V.  A. 
generators,  four  banks  of  transformers,  various  feeder  circuits. 
The  desk  comprises  a  pipe  framework  having  mounted  on  it 
nine  sections  of  marine  finished  slate  containing  the  various 
controllers,  indicating  lamps  and  similar  devices  while  a  separate 
instrument  frame  is  furnished  supported  by  pillars  from  the 
control  desk  and  containing  the  various  meters  needed  for  the 
installation. 

All  of  the  controllers  and  indicating  lamps  for  the  D.C.  sys- 
tem of  exciters  and  field  circuits  are  placed  on  the  front  of  the 


380         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

desk  while  the  controllers  and  similar  devices  for  the  A.C.  cir- 
cuits are  located  on  the  horizontal  top  of  the  desk. 

A  complete  miniature  bus  bar  system  is  placed  on  the  desk  to 
show  the  connections  made  by  the  various  breakers,  red  indi- 
cating lamps  being  connected  into  the  miniature  bus  bar  system 


FIG.  233. — Control  desk  with  round  pattern  meters  for  Inawashiro. 

in  such  a  manner  that  they  light  up  when  their  particular  breaker 
is  closed.  The  miniature  high  tension  bus  on  the  horizontal  slab 
of  the  desk  is  nickel  plated  and  the  corresponding  low  tension 
bus  is  polished  copper.  The  field  and  excitation  bus  is  distin- 
guished by  its  location  on  the  front  part  of  the  desk. 


CHAPTER  XV 
BUS  BARS  &  WIRING— GENERAL  INFORMATION 

Having  considered  the  apparatus  and  the  panels  that  are  used 
for  the  switching  equipment,  the  next  important  matter  to  be 
taken  up  is  that  of  the  bus  bars  and  wiring;  after  which  the 
arrangements  of  breaker  and  bus  structures  and  the  general 
layout  of  the  portion  of  the  power  plant  devoted  to  the  switching 
apparatus  will  be  discussed. 

Bus  Bars. — In  order  to  provide  facilities  for  utilizing  the  cur- 
rent developed  in  an  electrical  generating  station  to  the  best 
advantage,  it  is  customary  to  have  one  or  more  sets  of  circuits 
into  which  the  various  generators  deliver  their  current  and  from 
which  the  various  feeders  draw  their  current.  These  common 
circuits  are  known  as  "omnibus  bars"  or  "bus  bars." 

In  the  simplest  station  with  only  one  generator  and  only  one 
feeder  the  generator  connects  directly  to  the  feeder  but  in  practic- 
ally every  other  case,  with  more  than  one  feeder  or  more  than 
one  generator,  bus  bars  are  required. 

D.C.  Busses. — With  shunt-wound  D.C.  machines  it  is  nec- 
essary to  have  a  positive  bus  and  a  negative  bus;  while  if  two 
shunt  machines  are  run  in  series,  on  a  3-wire  system,  a  neutral 
bus  is  also  needed.  With  compound  wound  generators  an  equal- 
izer bus  is  required,  and  when  two  compound  wound  machines 
are  run  in  series  on  a  3-wire  system  or  when  a  compound 
wound  3-wire  D.C.  generator  is  used,  five  busses  are  needed — 
positive,  positive  equalizer,  neutral,  negative  equalizer  and 
negative.  For  2-wire  service  the  feeder  circuits  only  connect 
to  the  positive  and  negative  bus  bars  while  for  3-wire  service 
they  also  connect  to  the  neutral,  but  the  equalizer  busses  only 
connect  to  the  generators.  For  railway  circuits  with  ground 
return  the  feeders  only  connect  to  one  bus,  usually  the  positive, 
the  other  main  bus  (the  negative)  being  grounded  and  the  equal- 
zer  bus  merely  running  between  machines. 

A.C.  Busses. — In  single  phase  A.C.  systems  there  are  two 
busses,  in  2-phase  systems  usually  four  busses,  and  in  3-phase 

381 


382         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

usually  three  busses.  The  single-phase  system  may  be  3 -wire, 
the  2-phase  may  be  3-wire  or  5-wire,  while  the  3-phase  may  be 
4-wire  with  the  corresponding  number  of  bus  bars. 

Where  there  is  only  a  single  set  of  bus  bars  either  in  D.C. 
or  A.C.  stations  the  connections  are  said  to  be  arranged  on 
the  "single  throw"  system;  when  the  connections  can  be  made 
to  either  of  two  sets  of  bus  bars  the  system  is  spoken  of  as  "double 
throw",  while  if  the  connections  can  be  made  to  both  sets  of  bus 
bars  instead  of  only  to  either  set  the  system  is  spoken  of  as  the 
"selector  system."  Occasionally  three  or  more  sets  of  bus  bars 
are  used. 

If  there  is  only  one  set  of  bus  bars  but  switches  are  provided 
for  dividing  it  into  one  or  more  sections  it  is  spoken  of  as  a  sec- 
tioned bus.  Where  there  are  two  sets  of  these  sectioned  bus 
bars  connected  together  at  the  ends,  the  system  forms  a  ring  bus. 
In  many  high  voltage  plants  having  step  up  transformers  each 
generator  normally  connects  to  the  low  tension  side  of  its  own 
transformer  but  switches  are  provided  so  that  any  transformer  or 
generator  can  connect  to  a  bus,  such  a  bus  is  spoken  of  as  a  relay 
bus.  Where  a  number  of  feeders  connect  to  a  bus  which  in  turn 
connects  to  the  main  bus  through  a  switch  or  breaker  such  a  bus 
is  spoken  of  as  a  group  bus.  These  various  arrangements  are 
shown  on  the  diagrams  in  a  previous  chapter. 

Systems. — The  various  systems — single  bus,  double  bus,  relay 
bus,  group  bus,  etc.,  all  have  their  advantages  and  disadvantages. 
The  single  bus  is  naturally  the  cheapest,  simplest  and  least 
flexible  and  trouble  on  the  bus  is  apt  to  shut  down  the  plant. 
The  other  systems  are  more  flexible,  and  also  more  expensive  as 
they  require  more  apparatus.  In  every  installation  a  compro- 
mise must  be  effected  between  cost  and  flexibility,  and  each  case 
must  be  considered  on  its  own  merits.  In  small  low  voltage 
plants  bus  bar  trouble  is  almost  unknown  and  a  single-throw 
system  is  usually  employed.  In  high  voltage  large  capacity 
plants  although  bus  bar  trouble  is  rare,  a  more  flexible  system 
than  the  single  throw  is  often  advisable. 

Material. — Depending  on  the  current  and  voltage,  bus  bars 
may  be  made  of  wire,  rod,  tubing,  cable  or  strap,  either  bare  or 
insulated.  Solid  wire  is  seldom  used  for  more  than  200  amperes, 
rod  for  1000  amperes,  tubing  300-600,  cable  1000,  while  strap  is 
used  up  to  any  capacity.  Strap  for  bus  bars  possesses  several 
advantages  over  other  shapes,  the  chief  ones  being  the  ease  with 


BUS  BARS  AND  WIRING— GENERAL  INFORMATION      383 

which  additional  straps  may  be  installed  and  the  excellent  radi- 
ating surface  secured. 

Straps  of  different  sections  are  in  use,  a  typical  one  being 
3  inches  by  3^-inch.  Where  more  than  one  strap  is  required, 
a  space  is  kept  between  adjacent  bars  making  the  so-called 
laminated  bus.  The  usual  spacing  left  with  3  inches  by  ^-inch 
bars  is  %-inch.  The  connections  from  switches,  circuit  breakers, 
etc.,  to  the  bus  are  made  of  one  or  more  similar  straps  suitably 
interleaved  and  clamped  together. 

Current  Capacity. — Due  to  the  large  surface  exposed  in  com- 
parison to  the  section  of  copper  used,  comparatively  high  cur- 
rent density  may  be  employed  for  a  small  number  of  straps  with- 
out exceeding  a  safe  temperature  rise.  The  exact  amount  of 
current  to  be  carried  for  a  given  rise  depends  somewhat  on 
local  conditions,  ventilation,  etc.,  and  whether  the  bus  is  being 
used  for  direct-current,  25-cycle,  or  60-cycle  service,  and  the  tem- 
perature rise  is  not  the  same  for  different  parts  of  the  bar.  A 
typical  test  under  average  conditions,  60-cycle  service,  25-degree 
rise,  indicated  that  one  bar  would  carry  650  amperes,  two  bars 
1150  amperes,  three  1500,  four  1800,  five  2000,  six  2160,  showing 
that  due  to  "skin  effect,"  lack  of  ventilation,  etc.,  the  permissible 
current  density  falls  off  rather  rapidly  as  the  number  of  bars 
increases.  It  is  usually  necessary  to  interleave  the  phases  for 
60-cycle  service  to  carry  3000  amperes  or  more  without  an  ex- 
cessive amount  of  copper. 

Bus  Compartments. — In  large  capacity  A.C.  plants  of  13,200 
volts  or  less,  with  generators  connected  directly  to  the  bus,  the 
amount  of  current  that  can  be  concentrated  on  a  short  circuit 
is  something  enormous  and  every  precaution  has  to  be  taken  to 
prevent  trouble  from  spreading  if  it  ever  starts.  For  this  reason 
it  has  become  customary  to  employ  masonry  compartments 
and  cellular  construction  for  the  oil  circuit  breakers  and 
bus  bars. 

As  the  main  idea  of  the  cellular  scheme  is  to  provide  an  insulat- 
ing fireproof  barrier  between  leads  of  opposite  potential  in  heavy 
capacity  plants  of  13,200  volts  or  less  the  material  to  be  used  for 
the  structures,  barriers,  etc.,  is  of  the  utmost  importance.  The 
vertical  walls  and  septums  of  the  circuit-breaker  and  bus  bar 
structures  are  usually  built  of  brick  or  concrete  while  the  horizontal 
shelves  between  the  bus  bars  are  ordinarily  made  of  concrete, 
soapstone,  slate  or  marble.  In  some  instances  the  bus  bar  struc- 


384         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

tures  have  been  made  of  asbestos  lumber,  transite  or  similar 
material. 

Brick  Work. — The  brick  used  for  structural  work  of  this  kind  is 
usually  a  good  class  of  pressed  brick,  fire  brick  or  enameled  brick 
put  up  with  cement  mortar  and  presenting  a  fine  appearance.  In 
order  to  keep  down  the  cost,  it  is  sometimes  arranged  to  use  the 
finer  grades  of  brick  for  such  portions  of  the  structure  as  are 
visible  from  the  operating  room  or  noticeable  to  the  average 
visitor  while  a  cheaper  grade  is  used  for  such  other  parts  as  are 
normally  not  seen.  The  advantages  of  brick  for  this  class  of 
work  are  that  it  has  ample  strength  to  support  the  weight  and  to 
stand  the  jar  of  opening  of  a  heavy  breaker,  and  it  is  easy  to 
secure  good  bricklayers  in  almost  any  locality.  Its  disadvant- 
ages are  chiefly  due  to  its  relatively  fixed  dimensions,  the  difficulty 
of  reinforcing  thin  walls  of  any  considerable  height  and  the  trou- 
ble experienced  in  locating  conduits  for  control  leads,  etc.,  as 
well  as  the  fact  that  it  is  practically  impossible  to  make  the  hori- 
zontal shelves  of  the  same  material  as  the  vertical  walls  when  brick 
is  used. 

Concrete. — This  possesses  most  of  the  advantages  of  brick 
without  the  disadvantages  of  relatively  fixed  dimensions  and 
as  it  can  be  easily  reinforced  and  can  be  made  into  horizontal 
shelves  for  bus  bar  work  it  is  rapidly  becoming  a  favorite  material 
for  such  structures.  When  concrete  is  used  it  is  a  simple  matter 
to  imbed  the  conduit  for  the  control  leads,  the  tie  rods  for  the 
breakers,  the  bolts  for  switch  bases,  transformers,  etc.  in  the 
structure.  Concrete,  however,  is  somewhat  more  apt  to  absorb 
moisture  than  brickwork  but  when  dry  is  a  comparatively  good 
insulator  and  resists  the  destructive  effects  of  an  arc  as  well  as 
anything  used  for  the  purpose. 

Shelves. — Horizontal  shelves  between  bus  bars  have  been 
made  of  marble,  slate,  soapstone,  sandstone,  concrete  or  similar 
material  and  historically  they  have  been  used  about  in  the  order 
named  which  is  also  the  order  of  their  decreasing  cost.  Marble 
is  undoubtedly  the  best  material  as  far  as  insulation  and  absorp- 
tion qualities  go,  but  its  high  cost  and  its  crumbling  when  exposed 
to  a  bad  arc  has  caused  the  adoption  of  cheaper  materials  of 
slightly  poorer  insulating  qualities.  Slate,  the  next  material 
tried,  is  a  very  uncertain  insulator  for  high  voltage  work  and  it 
has  been  generally  superseded  by  soapstone,  sandstone  or  con- 
crete. Where  space  is  at  a  premium,  soapstone  is  used  almost 


BUS  BARS  AND  WIRING— GENERAL  INFORMATION      385 

exclusively  as  it  can  be  drilled,  machined,  etc.,  and  smaller 
clearance  distances  can  be  used  than  would  be  permissible  with 
sandstone  or  concrete.  Where  there  is  a  chance  to  secure  a 
reasonable  distance  between  bare  metal  parts  and  the  shelves 
or  barriers,  concrete,  either  plain  or  reinforced,  can  be  used  to 
advantage. 

Between  disconnecting  switches  and  in  such  places  where  the 
barrier  wall  does  not  carry  any  additional  weight,  asbestos  board, 
wire  glass,  etc.  has  sometimes  been  used. 

Enclosures. — Masonry  structures  for  bus  bar  work  are  made 
either  semi-enclosed  or  entirely  enclosed.  In  the  former  case 
the  wall  of  the  structure  which  separates  the  horizontal  bus  bars 
and  the  vertical  connections  is  made  practically  continuous. 
The  back  of  the  bus  bar  shelves  are  built  into  this  wall  while 
pilasters  properly  spaced  support  them  in  the  front.  Except 
for  these  pilasters  the  bus  bar  structure  is  open  in  the  front 
and  the  septums  in  the  rear  that  separate  the  leads  are  usually 
left  open.  This  scheme  leaves  the  bus  bars  and  connections 
readily  accessible  and  well  ventilated  but  makes  it  possible  for  a 
careless  visitor  or  attendant  to  come  in  contact  with  the  bus  or 
connection. 

A  modification  of  this  scheme  uses  a  continuous  wall  instead  of 
pilasters  as  a  support  for  the  front  of  the  shelves  and  the  bus  bars, 
connections,  etc.,  are  almost  completely  enclosed  except  for  open- 
ings provided  with  doors  at  the  supports,  contacts,  etc.  With 
this  arrangement  it  is  impossible  for  any  one  to  touch  any  live 
metal  parts  without  removing  a  door,  but  the  busses,  connec- 
tions, etc.,  are  not  so  accessible  or  so  well  ventilated  as  with  the 
more  open  arrangement. 

Leads. — Where  the  leads  pass  through  the  floor  or  the  back 
wall  of  a  bus  bar  structure,  either  of  two  schemes  may  be  adopted. 
With  the  first,  porcelain  bushings  are  used  to  give  the  necessary 
insulation  while  with  the  other  scheme  holes  of  generous  dimen- 
sions are  made  and  the  lead  run  through  the  middle  of  this  hole. 
In  one  case  porcelain  insulation  is  used  and  in  the  other  air. 
The  former  makes  a  tighter  joint  with  less  likelihood  of  smoke  or 
flame  passing  from  one  compartment  to  the  next  but  is  more  ex- 
pensive and  more  subject  to  insulation  trouble  than  the  latter. 

Connections. — For  bus  bars  and  connections  where  the  cur- 
rents exceed  600  or  800  amperes  it  is  usual  to  employ  laminated 
copper  straps  while  for  smaller  currents  cable,  wire,  rod,  or  tubing 


386         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

is  used.  Cable,  and  to  a  certain  extent  wire,  is  used  for  con- 
nections involving  bends  or  long  runs  through  conduit,  while 
for  straight  runs  or  simple  bends  rod  or  tubing  can  be  used. 
Tubing  while  more  costly  than  rod  or  wire  for  the  same  section 
is  stiffer  and  can  often  be  flattened  out  for  making  connections  to 
studs,  bars,  etc.  without  the  necessity  of  additional  terminals. 

Laminated  Bus. — One  of  the  advantages  of  the  laminated 
copper  strap  is  the  large  amount  of  radiating  surface  secured 
with  the  minimum  amount  of  material,  and  the  readiness  with 
which  it  is  possible  to  taper  the  bus  bars  so  as  to  utilize  the  ma- 
terial to  the  best  advantage  adjusting  the  capacity  of  the  bus  to 
the  total  amount  that  will  have  to  be  carried  at  any  one  point. 

Another  great  advantage  is  the  facility  with  which  additional 
strap  may  be  added  if  it  is  desired  to  increase  the  capacity  of  the 
bus  at  any  time.  Another  advantage  is  the  ready  means  by  which 
connections  can  be  made  if  laminated  copper  straps  are  used 
which  will  interleave  with  the  bus,  and  which  connect  the  bus  to 
the  studs  of  disconnecting  switches,  circuit  breakers  or  similar 
appliances. 

Supports. — As  supports  for  the  low  tension  bus  bar,  insulators 
of  various  kinds  have  been  designed,  these  usually  being  made  of 
porcelain  either  in  the  shape  of  cylindrical  or  conical  pillars,  or 
in  the  form  of  petticoat  insulators  depending  on  the  voltage  of 
the  circuit. 

Low  tension  bus  bars,  when  not  too  heavy,  can  be  supported  by 
the  wall  bushing  for  the  lead.  For  heavier  work,  or  where  bush- 
ings are  not  used,  the  bus  bars  are  supported  on  porcelain  pillars, 
petticoat  insulators,  and  similar  devices  resting  on  the  bus  bar 
shelf,  or  attached  to  the  wall. 

Bus  Stresses. — In  the  larger  generating  stations,  due  to  the 
tremendous  values  of  short-circuit  current  resulting  from  the 
size  and  number  of  turbogenerators  represented  in  present  day 
station  practice,  close  attention  must  be  given  to  the  adequacy 
of  the  bus  bar  supports.  Various  curves  and  formulae  have  been 
deduced  for  the  purpose  of  calculating  the  mechanical  strain  on 
bus  bar  supports  at  the  instant  of  short  circuit.  A  typical  for- 
mula is  the  following: 

F  =  .27  X  K.V.A.2  divided  by  A  X  V2  X  Z2  where 
F  =  maximum  force  exerted  in  pounds  per  foot  of  bus. 
K.V.A.  =  normal  rating  of  the  station  including  all  synchronous 
apparatus. 


BUS  BARS  AND  WIRING— GENERAL  INFORMATION      387 


388         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

A  —  distance  between  busses  in  inches. 

Z  =  impedance  in  per  cent,  expressed  in  decimals  to  the 

point  of  short  circuit. 
V  =  line  voltage. 

Fig.  234  and  235  are  graphic  representations  of  this  for- 
mula. In  using  this  formula  a  typical  example  with  150,000 
K.V.A.  station  capacity  at  6600  volts,  8  per  cent,  reactance 
gives  a  maximum  force  on  the  bus  bars  per  foot  of  length,  735 
Ibs.  with  30-inch  spacing  between  bars,  1470  Ibs.  with  15-inch 
spacings  between  bars.  With  four  feet  between  bus  supports 
each  bus  support  would  have  to  stand  a  strain  of  2940  Ibs.  if 
the  busses  are  30  inches  on  centers,  5880  Ibs.  if  the  busses  are 
15  inches  on  centers.  For  heavy  duty  of  this  kind,  multi-point 
supports  are  frequently  used. 

For  supports  of  high  tension  bus  bars  and  connections  it  is 
customary  to  employ  high  tension  insulators  of  the  pillar  type, 
pin  type,  or  suspension  type,  depending  on  the  voltage. 

Extra  High  Tension. — Where  the  generators  connect  through 
separate  transformers  giving  voltages  from  22,000  to  154,000  or 
even  higher,  the  question  of  enclosing  the  bus  bars  and  wiring 
for  the  high  tension  circuits  becomes  an  entirely  different  proposi- 
tion. 

Some  engineers  were  originally  of  the  opinion  that  the  cellu- 
lar construction  should  be  used  for  large  capacity  circuits  of  any 
voltage,  and  bottom  connected  breakers  have  been  designed  that 
work  in  well  with  the  enclosed  bus  bar  construction  for  high 
voltage  plants. 

Open  Construction. — The  almost  universal  American  opinion 
at  present  is  that  the  open  system  of  wiring  is  preferable  for  any 
voltage  higher  than  that  for  which  generators  can  be  conven- 
iently wound.  It  is  based  on  the  following  reasons: 

First. — The  violence  of  an  arc  and  the  destructive  effect  of 
short  circuits  depends  on  the  amount  of  current  available  at  that 
point.  While  fireproof  barriers  and  cellular  construction  are 
required  on  large  capacity  plants  of  comparatively  low  voltage, 
they  are  unnecessary  for  higher  voltage  plants  of  the  same  or 
even  larger  capacity. 

Second. — The  distance  from  wire  to  ground  has  to  be  greatly 
reduced  over  what  could  be  obtained  with  open  wiring  in  the 
same  space  as  the  fireproof  barriers  offer  a  more  or  less  perfect 


BUS  BARS  AND  WIRING— GENERAL  INFORMATION      389 


390         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

ground  for  high  voltage  circuits  and  the  higher  the  voltage  the 
more  perfect  the  ground. 

Third. — A  more  expensive  building  and  costly  construction 
are  usually  needed  for  enclosed  bus  bars  and  wiring  than  are 
required  for  open  wiring. 

Fourth. — Inspection  and  repairs  are  more  difficult  for  bus  bars, 
wiring,  disconnecting  switches  and  similar  appliances  that  are 
boxed  in  masonry  compartments,  and  are  only  visible  and  ac- 
cessible by  the  removal  of  doors,  than  if  everything  is  in  plain 
sight.  Inspection  will  be  more  frequent  and  thorough  and  incipi- 
ent trouble  will  be  noticed  far  sooner  with  open  wiring  than  with 
enclosed,  as  the  station  attendant  in  a  few  minutes  walk  can  see 
everything  and  will  not  have  to  remove  many  doors  and  visit 
two  or  three  floors  to  examine  the  condition  of  the  apparatus. 

In  most  cases  the  desirable  features  of  the  open  system  of 
wiring  for  high  voltage  can  best  be  secured  by  the  use  of  outdoor 
transformers  and  switch  gear. 

Tubing. — For  extremely  high  voltages  with  the  corresponding 
small  current,  copper  tubing  for  bus  bars  and  connections  has 
many  advantages  over  rods,  wire  or  strap,  these  advantages 
being  principally  increased  stiffness  for  the  same  amount  of 
material,  large  and  effective  radiating  surface  and  the  facility  of 
making  connections  by  flattening  out  the  tubing  at  the  point 
desired  and  bolting  the  tubing  together  at  such  points.  Tubing 
of  approximately  1  inch  outside  diameter  is  not  apt  to  be  troubled 
by  the  brush  discharge  or  corona  effect  that  is  sometimes  noted 
with  small  wires  or  strap  having  sharp  edges  when  used  on  ex- 
tremely high  voltage  circuits.  In  many  cases  standard  iron 
tubing  is  employed. 

Supports. — For  supports  for  such  high  tension  bus  bars  and 
connections  it  is  customary  to  employ  line  insulators  either  of 
the  pillar  type,  pin  type,  or  suspension  type,  depending  on  the 
voltage. 

Connections. — For  the  connections  between  generators,  trans- 
formers, feeder  circuits  and  their  switching  gear,  it  is  occasionally 
possible  to  use  bare  copper  conductors,  although  in  most  cases 
particularly  for  the  connections  between  the  generators,  the 
low  tension  side  of  step  up  transformers  and  their  switch  gear, 
insulated  wire  or  cables  are  better  adapted  for  the  actual  arrange- 
ment of  the  station. 

Cables. — On  all  circuits  of  more  than  200  amperes  the  leads 


BUS  BARS  AND  WIRING— GENERAL  INFORMATION      391 

usually  consist  of  cables,  the  number  and  size  depending  on  the 
current  to  be  carried  and  other  considerations.  It  is  often  practi- 
cable to  use  the  same  size  of  cable,  e.g.,  500,000  C.M.  for  all  the 
main  connections  in  one  plant,  using  as  many  cables  in  multiple 
as  may  be  required,  and  in  this  manner  utilizing  the  cable  to 
better  advantage  than  if  each  circuit  had  different  sizes  of  leads. 
Proper  terminals  can  always  be  supplied  on  the  switchboard  or 
machine  to  suit  any  reasonable  cable  requirements.  The  sizes 
of  cable  used  should  usually  correspond  with  the  carrying  capaci- 
ties as  given  by  the  National  Board  of  Fire  Underwriters  unless 
there  are  considerations  of  excessive  line  drop  in  a  long  feeder  or 
some  other  reason  for  departing  from  their  regulations. 

Underwriters. — As  far  as  possible  all  wiring,  etc.,  on  switch- 
boards strictly  corresponds  with  the  requirements  of  the  National 
Board  of  Fire  Underwriters,  but  it  has  been  found  impracticable 
to  attempt  to  wire  up  the  back  of  switchboards  used  on  voltages 
above  600  with  fireproof  wire  owing  to  the  poor  insulating  quali- 
ties of  the  fireproof  covering  and  the  consequent  necessity  of 
stripping  back  this  braid  for  several  inches  from  all  terminals, 
etc.,  on  the  back  of  the  board. 

CONTROL  AND  INSTRUMENT  CABLE 

Multiple  Cable. — For  the  connections  between  series  and  shunt 
transformers,  their  instruments  and  relays,  and  between  the 
controlling  devices,  and  the  circuit  breakers,  switches,  etc.,  that 
are  controlled,  it  is  customary  in  American  practice  to  supply 
multiple  conductor  cables,  each  conductor  being  provided  with 
distinctive  braid  to  facilitate  the  more  ready  checking  of  the 
wiring  after  it  is  installed.  This  multiple  conductor  cable  is 
usually  made  either  with  a  fireproof  braid  or  with  a  lead  cover, 
and  is  frequently  run  in  iron  pipe  conduit. 

As  the  instruments  and  control  switches  for  electrically  op- 
erated switchboards  are  usually  located  some  distance  from  the 
meter  transformers,  circuit  breakers,  rheostats  and  other  acces- 
sories, it  is  necessary  to  use  connecting  leads  of  varying  lengths. 
For  this  purpose,  multiple  conductor  cables  are  used. 

Size  of  Cable  Required. — The  sizes  of  conductors  generally 
used,  where  lengths  do  not  exceed  500  feet,  are  as  follows: 

For  current  transformer  circuits,  each  lead  should  be  equivalent 
to  19,500  circular  mils  and  for  very  short  runs  10,000  circular 


392         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


mils.  For  potential  transformer  circuits,  each  lead  should  be 
equivalent  to  10,000  or  6,000  circular  mils. 

For  small  solenoid  operated  circuit  breakers,  closing  coil  leads 
should  be  equivalent  to  19,500  circular  mils;  tripping  coil  and  in- 
dicator leads  equivalent  to  6000  circular  mils;  return  circuit  being 
same  size  as  closing-coil  lead,  either  in  same  cable  or  separate. 

For  large  oil  circuit  breakers  on  control  circuits  of  125  volts 
or  lower,  it  is  sometimes  considered  advisable  to  use  a  heavier 
closing  lead.  In  every  case  it  is  advisable  to  carefully  check  the 
drop  in  the  closing  circuit  to  insure  proper  operation  of  the 
breaker,  as  in  some  cases  very  heavy  leads  will  be  required. 
When  a  relay  switch  is  used,  the  lead  from  the  control  switch  is 

RUBBER-INSULATED,   BRAID-COVERED,   WEATHERPROOF  AND  FLAMEPROOF 
MULTIPLE-CONDUCTOR  CABLES  FOR  AUXILIARY  CIRCUITS 


Number 
of  con- 
ductors 

Stranding  of  each 
conductor,  inch 

Circular 
mils 

Diameter,  inches 

Approx. 
wt.,  Ibs.  per 
1000  ft. 

Bare 
copper 

Over  outer 
braid, 
maximum 

2 

19  of  0.0179 

6,000 

0.0895 

0.57 

150 

2 

19  of  0.0226 

10,000 

0.113 

0.62 

195 

2 

19  of  0.032 

19,500 

0.160 

0.78 

325 

3 

19  of  0.0179 

6,000 

0.0895 

0.61 

190 

3 

19  of  0.0226 

10,000 

0.113 

0.66 

225 

3 

19  of  0.032 

19,500 

0.160 

0.84 

430 

3 

One  19  of  0.032 

19,500 

0.160 

0.70 

230 

Two  19  of  0.0179 

6,000 

0.0895 

3 

One  37  of  0.0359 

47,500 

0.251 

0.81 

415 

Two  19  of  0.0179 

6,000 

0.0895 

4 

19  of  0.0179 

6,000 

0.0895 

0.66 

210 

4 

19  of  0.0226 

10,000 

0.113 

0.72 

300 

4 

19  of  0.032 

19,500 

0.160 

0.92 

540 

4 

One      19  of  0.032 

19,500 

0.160 

0.76 

375 

Three  19  of  0.0179 

6,000 

0.0895 

4 

Two  19  of  0.032 

19,500 

0.160 

0.76 

375 

Two  19  of  0.0179 

6,000 

0.0895 

5 

19  of  0.0179 

6,000 

0.0895 

0.75 

260 

5 

19  of  0.0226 

10,000 

0.113 

0.82 

350 

5 

Two     19  of  0.032 

19,500 

0.160 

0.86 

450 

Three  19  of  0.0179 

6,000 

0.0895 

6 

19  of  0.0179 

6,000 

0.0895 

0.80 

385 

6 

19  of  0.0226 

10,000 

0.113 

0.88 

500 

6 

19  of  0.032 

19,500 

0.160 

1.12 

760 

7 

19  of  0.0179 

6,000 

0.0895 

0.80 

420 

7 

19  of  0.0226 

10,000 

0.113 

0.88 

540 

BUS  BARS  AND  WIRING— GENERAL  INFORMATION      393 


only  large  enough  for  the  operating  current  in  the  relay  switch, 
for  which  purpose  6,000  circular  mil  cable  is  usually  adequate. 

For  engine  governor  control  or  electrically  operated  rheostat 
control,  each  lead  should  be  equivalent  to  10,000  or  6,000  circu- 
lar mils;  three,  four  or  six  leads  being  used,  as  required.  The 
cables  listed  below  are  particularly  adapted  to  the  diverse  require- 
ments of  switchboard  service. 

Insulation. — Each  individual  conductor  is  insulated  for  600- 
volt  service  and  is  covered  with  braid  with  an  identifying  color. 
The  insulated  conductors  are  assembled  and  covered  with  a 
layer  of  tape  and  an  outer  braided  covering  or  lead  sheath. 
The  outer  covering  of  the  cable  selected  depends  upon  the  nature 
of  the  installation. 

RUBBER-INSULATED,   LEAD-COVERED,   SINGLE   AND   MULTIPLE-CONDUCTOR 
CABLES  FOR  AUXILIARY  CIRCUITS 


Number 
of  con- 
ductors 

Stranding  of  each 
conductor,  inch 

Circular 
mils 

Diameter,  inches 

Approx. 
wt.,  Ibs.  per 
1000  ft. 

Bare 
copper 

Over  outer 
Braid 
maximum 

1 

19  of  0.0226 

10,000 

0.113 

0.37 

390 

1 

19  of  0.032 

19,500 

0.160 

0.45 

530 

1 

37  of  0.0285 

30,000 

0.200 

0.49 

600 

1 

37  of  0  .  0359 

47,500 

0.251 

0.55 

720 

2 

19  of  0.0179 

6,000 

0.0895 

0.65 

600 

2 

19  of  0.0226 

10,000 

0.113 

0.69 

735 

2 

19  of  0.032 

19,500 

0.160 

0.88 

930 

3 

19  of  0.0179 

6,000 

0.0895 

0.68 

715 

3 

19  of  0.0226 

10,000 

0.113 

0.73 

805 

3 

19  of  0.032 

19,500 

0.160 

0.94 

1,180 

4 

19  of  0.0179 

6,000 

0.0895 

0.73 

800 

4 

19  of  0.0226 

10,000 

0.113 

0.79 

915 

4 

19  of  0.032 

19,500 

0.160 

1.02 

1,400 

4 

One      19  of  0.032 

19,500 

0.160 

0.86 

1,025 

Three  19  of  0.0179 

6,000 

0.0895 

4 

Two  19  of  0.032 

19,500 

0.160 

0.94 

1,200 

Two  19  of  0.0179 

6,000 

0.0895 

5 

19  of  0.0179 

6,000 

0.0895 

0.82 

1,200 

5 

19  of  0.0226 

10,000 

0.113 

0.92 

1,300 

5 

Two     19  of  0.032 

19,500 

0.160 

0.90 

1,400 

Three  19  of  0.0179 

6,000 

0.0895 

0.90 

6 

19  of  0.0179 

6,000 

0.0895 

0.90 

1,040 

6 

19  of  0.0226 

10,000 

0.113 

1.10 

1,200 

6 

19  of  0.032 

19,500 

0.160 

1.25 

1,700 

7 

19  of  0.0179 

6,000 

0.0895 

0.90 

1,075 

7 

19  of  0.0226 

10,000 

0.113 

1.10 

1,200 

394         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Colors  of  Leads. — The  colors  used  by  one  manufacturer  in 
identifying  the  individual  conductors  are  as  follows:  First, 
black;  second,  white;  third,  red;  fourth,  green;  fifth,  yellow; 
sixth,  blue;  seventh,  yellow  and  green.  For  example,  a  four 
conductor  cable  requires  the  use  of  the  first  four  colors,  black, 
white,  red  and  green. 

When  conductors  of  different  sizes  are  used  in  a  multiple  con- 
ductor cable,  the  sequence  of  colors  given  above  is  followed  in  the 
order  of  the  capacities,  the  largest  conductors  having  a  black 
braid,  the  next  largest  a  white  braid,  etc. 

BUS  SUPPORTS 

Early  Types. — In  the  earlier  station  designs  the  use  of  petti- 
coat insulators  mounted  on  pins  for  supporting  high  tension  bus 
bars  and  wiring  was  practically  imperative,  owing  to  the  lack  of 
supports  specially  designed  to  meet  the  conditions.  This  prac- 
tice was  quite  general  and  in  some  instances  is  still  standard, 
especially  when  extensions  to  old  work  are  necessary.  The  use 
of  petticoat  or  line  insulators  had  the  advantage  of  employing 
a  standard  part  usually  available  or  easily  secured. 

Progress. — There  were,  however,  many  objections  to  their 
use,  especially  when  compactness,  flexibility  and  neat  appear- 
ance of  bus  bar  work  were  important.  The  petticoat  type  of 
insulator  support  is  not  well  adapted  for  horizontal  mounting, 
and  for  installations  where  a  back  connected  type  is  necessary 
the  petticoat  form  cannot  be  used  to  advantage.  It  is  not  easily 
inspected  or  cleaned  and  in  bus  bar  compartments  the  danger  of 
dust  or  dirt  accumulation  on  the  inner  petticoat  surface  is  appa- 
rent. Owing  to  manufacturing  difficulties,  it  is  practically  im- 
possible to  secure  uniform  dimensions  of  petticoat  insulator 
grooves,  heights,  etc.,  and  as  a  result  the  general  "line  up" 
of  the  conductor  or  bus  is  apt  to  be  irregular.  The  large  space 
required  is  also  frequently  objectionable,  especially  when  bus 
bar  or  wiring  compartments  are  used. 

Pillars. — As  station  design  progressed  the  bus  bar  or  high  ten- 
sion wiring  supports  began  to  receive  closer  attention,  first  by 
European  and  then  by  American  engineers.  The  earlier  Euro- 
pean designs  comprised  a  corrugated  pillar  having  recesses  at 
both  ends  into  which  were  rigidly  cemented  the  desired  fitting 
to  clamp  a  bus  bar,  mount  on  pipe  frame  work  or  flat  support. 


BUS  BARS  AND  WIRING— GENERAL  INFORMATION      395 

Cementing. — The  practical  objection  to  this  early  foreign 
standard  was  that  the  rigidly  cemented  fittings  and  insulators 
resulted  in  an  inflexible  unit,  difficult  to  install.  In  case  of 
changes  in  the  number  or  size  of  busses,  necessity  of  substituting 
pipe  work  for  flat  base  pins,  etc.,  the  limitations  became  very  ap- 
parent, as  it  was  necessary  to  remove  the  entire  unit,  substituting 
a  second  complete  unit  in  its  place.  In  short,  the  construction 
employed  in  the  early  European  designs  was  electrically  good  but 
mechanically  inconvenient,  expensive  and  cumbersome.  It  was 
a  rigid,  inflexible  design  not  well  adapted  to  American  practice. 

Another  serious  objection  to  the  original  type  was  that  it  was 
impossible  for  manufacturers  or  users  to  carry  a  complete  stock, 
as  the  fittings  of  each  particular  size  were  rigidly  cemented  in 
place  and  parts  could  not  be  interchanged.  Factory  shipments 
were,  therefore,  slow  and  the  user  always  had  an  equipment  devoid 
of  interchangeable  features. 

Post  Type. — The  next  step  in  design  and  manufacture  of  bus 
bar  supports  was  the  "post  type,"  consisting  of  a  corrugated 
post  provided  with  removable  top  and  bottom  clamp  fittings. 
This  improved  design  eliminated  the  interchangeability  limita- 
tions of  the  older  pillar  type,  having  rigidily  cemented  fittings, 
so  the  parts  could  be  adjusted  or  replaced  as  desired.  The  dis- 
advantage of  the  "post  type"  support  was  that  the  method 
adopted  of  attaching  the  top  and  bottom  clamps  on  the  outside 
of  the  insulator  materially  cut  down  the  leakage  surface.  As  the 
clamps  extended  over  at  least  one  corrugation,  this  design  also 
necessitated  greater  dimensions  in  order  to  maintain  the  same 
factor  of  safety  secured  with  the  older  form  of  cemented  "pillar 
type  supports." 

Clamps. — The  clamps  at  top  and  bottom  were  also  consider- 
ably wider  than  employed  with  the  older  "pillar  supports," 
necessitating  wider  spacings  between  insulators,  greater  clear- 
ances for  height,  use  of  larger  bus  bar  compartments  and  as  a 
final  result  a  larger  substation  or  station  building. 

These  clamped  supports  are  made  by  various  builders  with 
different  features.  Those  of  the  Westinghouse  Company  have 
been  selected  as  illustrating  the  general  type. 

Westinghouse  Supports.— Type  P  bus  supports  of  the  West- 
inghouse Electric  &  Manufacturing  Company,  with  corru- 
gated insulators  consist  essentially  of  an  insulator  with  suitable 
bus  and  mounting  fixtures  clamped  on. 


396         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

The  insulators  are  made  of  porcelain  by  wet  process  and  have  a 
brown  mahogany  glaze.  The  insulators  are  corrugated  to  insure 
ample  creepage  surface  under  service  conditions.  The  fittings 
are  made  of  malleable  iron  or  cast  brass  and  have  a  high-grade 
dull  black,  baked  finish.  Interchangeability  of  fittings  on  porce- 
lains of  different  voltage  but  of  same  diameter  of  head  or  base  is 
provided. 

Stresses. — Mechanical  stresses  due  to  short  circuits  on  the 
bus  bars  must  be  considered  in  selecting  the  type  and  size  of 


FIG.  236. — Bus  bar  supports  with  braces. 

support.  These  short-circuit  stresses  may  depend  on  the 
maximum  ampere  load,  under  short-circuit  conditions,  the  dist- 
ance between  center  line  of  bus  bars  and  the  relative  location  of 
the  bus  bars. 

To  meet  these  varied  requirements,  several  sizes  of  insulators 
are  made  for  the  lower  voltages,  from  which  proper  selection 
may  be  made. 

Heavy  Supports. — Insulator  supports  for  extra  heavy  busses 
can  be  supplied,  when  desired,  with  insulator  braces  between  the 
bus  bars,  as  shown  in  Fig.  236.  The  complete  support  and  brace 
are  made  up  of  standard  parts.  This  arrangement  is  equally 
adaptable  for  frame  or  cell  mounting. 


BUS  BARS  AND  WIRING— GENERAL  INFORMATION      397 

Tests. — Voltage  tests  with  all  fittings  on  are  given  in  table 
below.  These  tests  are  ample  for  ordinary  applications  and  are 
well  within  the  requirements  of  the  recommendations  of  the 
American  Institute  of  Electrical  Engineers.  The  large  creepage 
surface  provided  by  the  corrugations  insures  the  ability  of  the 
insulator  to  stand  the  same  test  under  service  conditions. 


Maximum  service  voltage 
7,500 
15,000 
25,000 
35,000 
44,000 


One  Minute 
dry  test  volts 

20,000 

40,000 

65,000 

90,000 
115,000 


For  exceptional  installations  where  an  insulator  of  a  high  volt- 
age test  may  be  desired,  next  higher  maximum  service  class  may 
be  used. 

Fig.  237  shows  an  extra  heavy  duty  bus  arrangement,  busses 
vertically  mounted  in  same  horizontal  plane  with  barriers. 


FIG.  237. — Heavy  duty  bus  support. 

This  arrangement  employs  standard  supports  requiring  the 
same  number  as  is  ordinarily  used  for  single  supports,  but  so 
disposed  that  one  half  of  the  porcelains  are  in  compression  from 
short-circuit  stresses. 

Compression. — The  rating  of  the  supports  can  be  increased 
to  meet  the  demands  of  extra  heavy  duty,  by  so  locating  the 


398         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


supports,  that  some  of  them  will  always  be  in  compression  under 
short-circuit  stresses. 

A  series  of  typical  insulators  with  the  various  clamping  devices 
and  switchboard  details  is  shown  in  Fig.  238,  while  the  applica- 


FIG.  238. — Bus  fittings  &  details. 

tion  of  these  devices  and  various  standardized  details  as  furnished 
by  the  Westinghouse  Company  are  shown  in  Fig.  239. 

Delta-Star. — Other  makers  of  fittings  have  adopted  different 
methods  of  attaching  the  metal  parts  to  the  porcelain  insulators 
and  claim  certain  advantages  for  their  designs.  The  Delta- 


BUS  BARS  AND  WIRING— GENERAL  INFORMATION      399 

Star  Company  have  a  line  of  "Unit  Type  Bus  Bar  Supports" 
that  they  have  developed  and  which  they  consider  superior  to  the 
clamped  type  for  different  reasons,  given  below. 

Objections  to  Post  Type.— Owing  to  their  greater  weight  and 
size,  larger  and  heavier  and  more  expensive  supporting  struc- 
tures were  necessary  than  with  the  pillar  form.  For  moderate 
potentials,  22,000  volts  and  less,  the  "post  type"  insulators 
were  abnormally  large  and  heavy,  did  not  permit  of  a  neat 
construction  and  were  altogether  out  of  proportion  for  the  work 


FIG.  239. — Westinghouse  switchboard  details. 

to  be  accomplished.  While  the  "post  type"  insulator  was  an 
improvement  from  a  manufacturing  standpoint,  it  did  not  work 
out  so  advantageously  for  the  user,  especially  when  making 
extensions.  Owing  to  the  increased  size  and  weight  (necessitat- 
ing greater  clearances,  etc.)  it  was  frequently  an  impossibility 
to  install  the  "post  type"  in  existing  substations  or  wiring  sys- 
tems where  a  given  place  had  been  provided  for  future  extensions. 
Unit  Type. — The  problem  presented  by  modern  conditions 
was  then  given  close  attention  and  after  consulting  experienced 
power  house  engineers  the  final  standard  adopted  was  the  "  Unit 
Construction"  bus  bar  supports.  These  supports  have  all  the 
advantages  of  previous  types  with  none  of  the  disadvantages 


400         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


and  permit  of  a  flexibility  in  manufacture,  assembly  and  installa- 
tion impossible  to  obtain  in  the  older  forms. 

The  "Unit  Type"  wet  process  corrugated  porcelain  pillars 
are  recessed  at  each  end  and  provided  with  a  sanded  surface 
socket  in  which  is  cemented  a  malleable  iron  thimble,  threaded 
to  receive  the  proper  fittings  for  the  service  to  be  met.  The 
advantages  of  this  construction  will  be  quickly  appreciated  by 
engineers,  as  a  flat  base  mounting  can  quickly  be  converted  to  a 
pipe  frame  mounting,  etc. 


if] 


FIG.  240. — Unit  construction,  bus  bar  supports. 

Changes. — If  future  requirements  make  it  desirable  to  change 
bus  bar  sizes  it  is  simply  necessary  to  remove  the  original  fitting 
and  install  a  new  one  of  different  type  or  size. 

The  wet  process  insulators  are  finished  in  dark  brown  glaze, 
the  metal  parts  having  black  enamel  finish.  This  combination 
of  colors  insures  a  pleasing,  permanent  finish  corresponding  to 
other  high-grade  switchboard  and  bus  structure  equipment. 

The  "Unit  Construction"  has  an  additional  advantage  in  that 
bus  bar  supports  can  easily  and  quickly  be  reconstructed  for 
higher  "potentials  by  the  user.  A  good  example  of  this  desirable 
feature  is  shown  in  Fig.  240.  The  support  to  be  increased  in 
voltage  rating  is  shown  at  'A,'  the  insulator  unit  with  bus  bar 
clamp  removed  at  'B,'  the  additional  unit  is  in  position  at 
'C'  and  the  complete  assembly  is  shown  at  'D.'  This 


BUS  BARS  AND  WIRING— GENERAL  INFORMATION      401 

flexibility  of  design  will  be  fully  appreciated  if  it  becomes  nec- 
essary to  make  changes  in  the  bus  bar  construction. 

Bases. — The  seven  styles  of  bases  shown  in  Fig.  241  will  be 
found  to  meet  practically  every  condition  encountered  in  the 
installation  of  busses  and  general  station  wiring.  Special  bases 
to  meet  local  conditions  can  be  supplied. 


FIG.  241. — Bus  bar  base  fittings. 

Clamps. — Bus  bar  clamps  for  "Unit  Type"  supports  are 
shown  in  Fig.  242,  Type  '  I '  clamp.  The  type  '  I '  clamp  is  of 
the  two  bolt  form  designed  to  support  flat  copper  bars  in  a 
horizontal  position  on  horizontal  structures  or  in  a  vertical 
position  from  vertical  structures.  The  former  method  is  gener- 
ally used  in  enclosed  bus  bar  compartments  where  it  is  essential 
to  limit  the  height  of  the  compartment.  The  latter  method  is 


FIG.  242. — Bus  bar  clamps  for  unit  type  supports. 


more  applicable  to  open  bus  bar  work.     Other  clamps  for  differ- 
ent purposes  are  available  with  various  numbers  of  bolts. 

Bus  Switch. — The  "Unit  Type"  bus  switch  shown  in  Fig. 
14  of  Chapter  1  is  an  interesting  application  of  the  "Unit  Type" 
insulators.  This  switch  is  designed  to  clamp  directly  on  the  bus 
bar,  and  is  a  convenient  method  of  inserting  a  disconnect  between 
the  oil  switch  and  bus,  thus  securing  a  high  space  factor.  The 


402         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

adjustable  contact  and  holding  clamps  enable  the  switch  to  be  so 
located  that  a  short  run  is  secured  to  the  oil  circuit  breaker 
terminal.  This  type  of  switch  is  made  for  any  desired  capacity 
flat  or  round  bus. 

Outdoor  Units.— The  "Unit  Type"  idea  has  been  extended  to 
outdoor  equipment  for  all  commercial  voltages.  A  complete 
line  of  bus  bar  supports,  wiring  supports,  disconnecting  switches, 
choke  coils  and  fuse  mountings  have  been  developed. 

The  voltage  ratings  conform  to  the  standard  commercial 
pressure  of  6600,  13,200,  22,000,  33,000,  44,000  volts.  The 
following  tabulation  shows  the  insulation  strength  of  bus  bar 
supports  for  different  voltages. 

"UNIT  TYPE"  INSULATOR  CHARACTERISTICS 

Normal-rated  voltage  Tested  at  Normal  factor  of  safety 

6,600  volts  30,000  volts  Approx.  4  :  1 

13,200  volts  54,000  volts  Approx.  4  :  1 

22,000  volts  75,000  volts  Approx.  3  :  1 

33,000  volts  100,000  volts  Approx.  3  :  1 

44,000  volts  125,000  volts  Approx.  2%  :  1 

Wire  and  Cable. — For  the  main  connections  between  the 
various  parts  of  the  switch  gear  and  the  generators,  feeders,  etc., 
cables  or  wires  are  frequently  used  and  most  of  the  larger  manu- 
facturing and  operating  companies  have  standardized  their 
specifications  for  cables  and  wires.  These  naturally  differ  with 
different  concerns  but  in  most  cases  they  have  been  based  on 
specifications  adopted  by  the  National  Fire  Protection  Associa- 
tion or  some  similar  body.  In  most  cases  two  styles  of  rubber- 
insulated  braid-covered  cables  or  wires  are  available: — 1.  With 
one  weatherproof  braid.  These  are  known  as  Rubber-Insulated 
Braid-Covered  Wires  and  Cables.  2.  With  one  weatherproof 
braid  and  an  outer  flameproof  braid.  These  are  known  as 
Rubber-Insulated  Flameproof  Wires  and  Cables. 

Standards. — The  use  of  these  standards  in  the  selection  of 
wires  and  cables  will  greatly  facilitate  delivery  of  such  wires  and 
cables.  It  will  also  avoid  confusion  due  to  the  necessity  of 
following  special  material,  and  changing  the  dimensions  of 
bushings  and  terminals  to  fit  special  cables. 

Sizes. — In  order  to  keep  the  number  of  different  kinds  of 
cable  in  an  installation  within  reasonable  limits,  when  the  differ- 
ence in  insulation  thickness  required  for  different  voltages  is 


BUS  BARS  AND  WIRING— GENERAL  INFORMATION      403 

not  large,  it  is  well  to  use  the  heavier  insulation  for  both  voltages, 
and  to  furnish  a  cable  with  more  copper  than  is  required  for  a 
given  service  rather  than  to  order  a  special  size.  Where  cable 
of  a  given  size  is  required  to  have  flexible  stranding  for  some  work, 
it  is  better  to  use  it  where  a  stiff  stranding  would  be  satisfactory, 
unless  the  amount  of  stiff  stranded  cable  exceeds  1000  feet,  so 
as  to  warrant  ordering  it  special  for  use  on  the  installation  in 
question. 

In  ordering  600-volt,  rubber-insulated  wires  and  cables  from 
manufacturers'  stock,  specify  the  capacity,  "  National  Electrical 
Code  Standard,"  and  give  the  number  of  weatherproof  braids 
desired.  For  example,  61  of  .1145,  600-volt  Code  Std.  Cable 
with  two  weatherproof  braids. 

Bends  in  Cables. — Care  must  be  taken  to  see  that  the  curve 
about  which  the  cable  is  bent  is  large  enough  to  prevent  injury 
to  the  insulation.  The  radius  of  the  smallest  curve  about  which 
bending  is  recommended  for  cables  is  usually  given;  a  larger 
radius  is  much  preferable,  as  the  larger  the  radius  the  less  liability 
of  injury  to  the  insulation  at  the  bend. 

Three-Conductor  vs.  Single-Conductor  Cable. — For  generator 
leads,  where  the  current  is  small  enough  to  permit  the  use  of 
standard  three-conductor  cables,  these  are  to  be  preferred  to 
three  single-conductor  cables.  All  cables  carrying  heavy  cur- 
rents must  be  rigidly  supported  to  prevent  the  cables  being  dis- 
placed by  a  severe  short  circuit. 

Dry  Places. — Up  to  and  including  600  volts,  single  or  multiple 
conductor,  rubber-insulated,  or  varnished  cambric-insulated, 
flameproof  cables  should  be  used.  When  cables  are  mounted 
directly  upon  a  switchboard  panel,  the  slate  or  marble  panel  is 
considered  as  an  insulator  and  it  is  not  necessary  to  mount  the 
cables  upon  additional  insulators. 

For  service  over  600  volts  and  up  to  and  including  15,000  volts 
single  or  multiple-conductor,  rubber-insulated,  or  varnished  cam- 
bric-insulated, flameproof  cables  are  suitable.  The  flameproof 
covering  does  not  provide  much  insulation  and  therefore  should 
be  treated  as  a  conductor  and  stripped  back  a  sufficient  distance 
to  afford  ample  creepage  distance  for  the  potential  of  the  cir- 
cuit. When  the  cable  is  in  such  short  lengths  that  it  would  be 
necessary  to  strip  off  nearly  all  of  the  flameproof  covering  to 
obtain  the  necessary  creepage  distances  over  the  surface  of  the 
insulation,  cables  with  weatherproof  braid  may  be  used. 


404         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Small  wiring  for  transformers,  instruments,  etc.,  may  be  cleated 
directly  upon  marble  panels  for  circuits  of  not  over  2500  volts,  if 
suitable  creepage  distances  are  provided  between  conductors  and 
to  ground. 

No  standard  has  been  adopted  for  service  over  15,000  volts, 
some  engineers  demanding  full  insulation  for  the  line  voltage 
while  others  specify  bare  conductors. 

Wet  Places. — Up  to  and  including  600-volts  service  single  or 
multiple-conductor,  rubber-insulated,  or  varnished  cambric-insu- 
lated braid-covered  cables  can  be  used. 

For  service  over  600  volts  up  to  and  including  15,000  volts, 
single  or  multiple-conductor,  paper-insulated,  rubber-insulated  or 
varnished  cambric-insulated,  lead-covered  cables  are  recom- 
mended, cables  to  be  installed  without  insulators. 

When  it  is  necessary  to  use  braid-covered  cables,  they  may  be 
either  rubber,  or  varnished  cambric-insulated,  and  must  be 
mounted  on  insulators  suitable  for  the  voltage  service. 

No  standard  has  been  adopted  for  over  15;000-volts  service 
some  engineers  demanding  full  insulation  for  the  line  voltage 
while  others  specify  bare  conductors. 

Conduits. — Metal  and  bitumenized  fibre  conduits  can  be  used 
for  single  or  multiple-conductor,  rubber-insulated,  or  varnished 
cambric-insulated,  braid-covered  cables. 

When  single-conductor  cables  are  used  on  alternating-current 
circuits  in  metal  conduits,  all  of  the  phases  of  the  circuit  must  be 
installed  within  the  same  metal  conduit. 

Metal,  cement  and  tile  conduits  are  suitable  for  single  or  multi- 
ple-conductor, paper-insulated,  rubber-insulated,  or  varnished 
cambric-insulated,  lead-covered  cables. 

Bells. — End  bells  must  be  used  on  circuits  of  over  2500  volts, 
and  should  preferably  be  furnished  on  circuits  of  over  750  volts. 

Where  cables  are  supported  on  insulators  below  the  floor  (up 
to  and  including  15,000- volt  service)  and  there  is  likely  tobe'mois- 
ture,  as  on  the  ceiling  of  basements,  etc.,  the  following  practice 
is  advisable: 

Single  or  multiple-conductor,-paper-insulated,  rubber-insulated, 
or  varnished  cambric-insulated,  lead-covered  cables  are  recom- 
mended, cables  to  be  installed  without  insulators. 

When  it  is  necessary  to  use  braid-covered  cables,  they  may  be 
either  rubber  or  varnished  cambric-insulated,  and  must  be 
mounted  on  insulators  suitable  for  the  voltage  service. 


BUS  BARS  AND  WIRING— GENERAL  INFORMATION      405 

Lead-Covered  Cables. — In  all  cases,  lead-covered  cables  are 
good  for  continuous  service  with  lead  grounded  at  the  maximum 
voltage  for  which  they  are  listed.  The  varnished  cambric- 
insulated  wires  and  cables  have  insulation  in  accordance  with  the 
practice  of  the  responsible  cable  manufacturers.  The  under- 
writers have  not  yet  prepared  specifications  for  this  class  of  wires 
and  cables. 

All  rubber-insulated  wires  and  cables  purchased  under  speci- 
fications of  certain  manufacturers,  with  the  exception  of  multiple- 
conductor  cables,  lead-covered  cables,  and  a  few  special  cables 
are  provided  with  a  separator  of  cotton  yarn  or  paper  between 
the  rubber  insulation  and  the  copper  to  prevent  the  rubber  com- 
pound from  adhering  to  the  copper.  This  facilitates  stripping 
of  insulation  and  soldering  of  conductors  where  joints  are  to  be 
made. 


CHAPTER  XVI 


BREAKER  STRUCTURES 

Where  the  direct-control  switchboard  is  not  employed  but 
distant  control  oil  circuit  breakers  are  utilized  for  the  main  A.C. 
connections,  the  arrangement  of  the  breakers,  disconnecting 
switches,  bus  bars,  etc.,  is  of  great  importance,  and  on  the  proper 
location  of  these  devices  rests  the  satisfactory  performance  of 
the  equipment. 

Bus  Arrangements. — To  give  a  better  idea  of  the  difference 
between  the  panel  mounted  and  the  distant  control  arrangements 


FIG.  243. 


FIG.  244. 


some  typical  layouts  of  different  locations  for  breaker  and  bus 
are  shown.  Fig.  243  shows  panel  mounted  oil  breaker  with 
bare  bus  and  connections  for  service  at  voltages  up  to  750  volts, 
with  bus  directly  over  the  breaker  while  for  voltages  above  750 
it  becomes  desirable  to  have  the  bus  higher  than  the  head  of  the 
operator.  Fig.  244  shows  the  corresponding  schemes  using  the 
panel  frame  mounted  breakers  to  get  additional  clearance  and 
to  remove  the  breaker  from  the  rear  of  the  board.  This  panel 

406 


BREAKER  STRUCTURES  407 

frame  mounting  gives  a  better  construction,  in  that  connections 
from  circuit  breakers  to  bus  bars  are  more  nearly  direct  and  more 
space  is  available  for  taking  away  connecting  cables  to  panels 
and  for  mounting  switchboard  details.  Some  of  the  other 
advantages  are  the  following:  less  likelihood  of  oil  getting  on 
panels;  the  weight  of  breakers  is  carried  on  frame  instead  of  on 
panel;  the  rear  of  the  panels  is  more  accessible;  several  types  and 
capacities  of  breakers  have  interchangeable  mountings;  with 
narrow  panels  the  position  of  the  breaker  handle  is  not  restricted 
to  the  center  of  the  panel  so  that  knife  switches  and  handles  for 
remote  control  breakers  can  often  be  added  where  this  would  be 
impossible  with  direct  panel  mounting  unless  wider  panels  are 
used. 

Unit  Assemblies. — In  designing  the  bus  and  oil  circuit-breaker 
structures  illustrated,  endeavor  has  been  made  to  assemble  all 
the  apparatus  within  a  unit  space,  in  order  that  a  section  may  be 
considered  a  distinct  piece  of  apparatus  which  may  be  located 
as  a  unit  where  desired. 

The  enclosed  and  semi-enclosed  structures  are  designed  to  suit 
walls  and  barriers  of  concrete.  In  case  brick  structure  is  desired, 
the  dimensions  may  have  to  be  modified  slightly  to  suit  the  sizes 
of  brick  used. 

(a)  Open  Construction — Frame  Mounting. — Each  bus  and  cir- 
cuit-breaker structure  section  with  frame  mounting  breakers  (2400 
to  13,200  volts,  consists  of  a  1^-inch  pipe  framework  together 
with  necessary  mounting  brackets  and  supports  for  the  equip- 
ment, consisting  of  oil  circuit  breakers,  disconnecting  switches, 
instrument  transformers,  bus  bars,  and  connections. 

(6)  Open  Construction — Wall  Mounting. — When  desire'd,  equip- 
ments with  frame  or  wall  mounting  breakers  will  be  supplied  by 
the  switchboard  builder  with  framework  details  omitted,  and 
only  connections  from  circuit  breakers  to  bus  bars,  bus  bar  su- 
ports  and  terminals,  wall  braces,  and  brackets  necessary  to  adapt 
the  circuit  breakers  for  wall  mounting. 

(c)  Semi-Enclosed  Construction. — When  desired,  the  wall 
mounting  or  frame  mounting  breakers  may  be  suitably  enclosed 
and  barriers  added  between  the  busses,  forming  a  semi-enclosed 
structure.  Such  enclosures  usually  require  a  greater  distance 
between  adjacent  breakers.  When  the  equipments  are  to  be 
installed  in  this  manner,  it  is  usual  for  the  purchaser  to  provide 
the  complete  cells,  top  slab,  doors,  barriers  and  all  cell  material. 


408         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

(d)  Enclosed  Construction — Wall  Mounting. — The  wall  mount- 
ing breakers  may  be  enclosed  and  separate  fireproof  compartments 
provided  for  all  bus  bars  and  main  connections.     Equipments 
with  wall  mounting  breakers  may  be  installed  in  this  manner,  the 
purchaser  furnishing  all  material. 

(e)  Enclosed  Construction — Cell  Mounting. — Each  bus  and  cir- 
cuit breaker  structure  section  with  cell  mounting  breakers,  as 
usually  supplied  includes  a  complete  set  of  mounting  and  con- 
nection details,  switching  and  transformer  equipment,  and  cell 
mounting  breakers  suitable  for  an  enclosed  cellular  construction, 
wherein  there  is  provided  a  separate  compartment  for  each  cir- 
cuit-breaker pole,  bus  bar,  and  main  connection.     Tie  rods  and 
channel  iron  base,  when  necessary,  and  breaker  front  cell  doors 
are  also  included.     Doors  for  other  parts  of  the  structure  can  be 
furnished.     Structures  for  most  of  the  wall  or  frame  mounting 
breakers  may  also  be  designed  to  line  up  with  the  cell  mounting 
breakers. 

Frame  and  wall  mounting  breakers,  22,000  volts  and  over, 
which  are  usually  arranged  for  open  construction,  frame  mount- 
ing, are  also  suitable  for  open  construction,  wall  mounting,  and 
semi-enclosed  construction,  wall  mounting. 

Cell  mounting  breakers,  22,000  volts  and  over,  may  be  ar- 
ranged for  semi-enclosed  construction  or  enclosed  construction. 

Floor  mounting  breakers  are  designed  for  open  construction 
and  are  not  readily  adaptable  for  enclosed  or  semi-enclosed  con- 
struction, although  such  designs  are  possible  if  desired. 

Limits. — The  remote  mechanically  controlled  switchboard  is 
limited  in  capacity  by  physical  rather  than  electrical  character- 
istics. As  nearly  all  high  capacity  circuit  breakers  may  be 
arranged  for  remote  mechanical  control  as  well  as  electrical  op- 
eration, the  problem  becomes  one  of  mechanical  arrangement  in 
which  it  is  usually  very  easy  to  meet  the  electrical  requirements. 

The  choice  of  the  proper  form  of  structure  for  the  apparatus 
which  is  to  be  remote-controlled  and  the  satisfactory  arrange- 
ment of  the  apparatus  thereon  presents  a  more  difficult  problem 
than  does  the  design  and  arrangement  of  the  panels  themselves. 
The  reason  lies  in  the  many  practical  forms  of  structure,  and  the 
large  number  of  arrangements  of  the  apparatus  which  may  be 
made  upon  each  of  the  various  forms. 

Equipment. — The  following  apparatus  must  usually  be  con- 
sidered in  choosing  a  satisfactory  arrangement :  Circuit  breakers, 


BREAKER  STRUCTURES  409 

bus  bars  and  connections,  rheostats,  instrument  transformers, 
fuses  for  potential  transformer  primaries  and  for  main  wiring 
when  employed,  and  disconnecting  switches.  Before  a  proper 
choice  can  be  made,  a  complete  diagram,  including  all  main 
wiring  and  all  of  the  above  apparatus,  should  be  carefully  made, 
according  to  the  system  of  connections  which  has  been  adopted 
for  the  installation  under  consideration.  From  this  wiring 
diagram  should  be  selected  the  circuit  which  presents  the  most 
complications;  that  is,  the  greatest  number  of  disconnecting 
switches,  instrument  transformers,  etc.,  and,  with  the  various 
practical  forms  of  structure  in  mind,  an  arrangement  should  be 
worked  out  for  this  unit  of  the  structure.  If  the  remaining  cir- 
cuits have  the  same,  or  a  less  number  of  members  in  the  same 
relative  location  in  the  circuit  as  regards  the  oil  circuit  breakers, 
the  problem  is  solved  and  the  remainder  of  the  work  is  simply 
duplication.  If  the  members  in  some  circuits  appear  in  other 
locations  than  those  in  the  circuit  chosen,  each  differing  unit 
must  be  worked  out  individually,  with  a  view,  however,  of 
forming  them  into  a  symmetrical  and  uniform  structure.  The 
choice  of  arrangement  depends  upon  the  capacity  of  the  station, 
the  cost,  the  available  space,  the  voltage,  the  type  of  circuit 
breaker  chosen,  and  the  current  capacity  of  individual  circuits. 

Wall  Arrangement. — It  should  be  remembered  that  wall 
arrangement  may  be  more  costly  than  the  separate  frame  arrange- 
ment if  large  windows,  which  must  be  bridged  by  steel  work, 
occur  back  of  the  board.  Concrete  or  masonry  structures  may 
add  considerably  to  the  cost  of  floor  construction  and  support  on 
account  of  their  great  weight.  The  wall  mounting  arrange- 
ments occupy  the  least  space  but  have  the  disadvantage  of 
giving  accessibility  from  one  side  only.  For  this  reason  and 
because  of  the  great  increase  in  available  space  for  mounting 
various  members  of  the  assembly,  the  separate  mounted  struc- 
tures are  preferred  where  space  can  be  found. 

Breaker  Mountings. — There  are  two  kinds  of  circuit  breakers 
as  regards  their  mounting:  those  designed  for  wall  or  pipe  frame 
mounting  and  those  for  cell  mounting.  Any  of  the  former  may 
be  enclosed  in  cells  if  desired.  By  the  latter  is  meant  those 
circuit  breakers  assembled  from  unit  poles,  each  pole  being 
designed  to  occupy  a  separate  cell. 

Electric  Control. — All  the  advantages  gained  by  the  use  of 
hand  operated  remote  mechanical  control  breakers  over  switch- 


410         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

board-mounting  breakers  are  applicable  to  the  electrically 
operated  breaker  installations.  The  space  required  for  breakers 
and  bus  bars  for  a  given  capacity  will  be  practically  identical, 
but  due  to  the  absence  of  operating  rods,  bell  cranks,  etc.,  arrange- 
ments and  designs  of  structures  can  be  used  that  are  not  possible 
otherwise  and  that  present  various  adaptations  to  certain  desir- 
able building  designs,  which  are  out  of  the  question  with  hand 
operated  remote  control  breakers.  This  is  particularly  evident 
in  large  stations  where  high  tension  voltages  such  as  2400,  6600 
and  11,000  are  used  for  generators,  and  where  extra  high  tension 
voltages  such  as  22,000,  44,000,  66,000,  etc.,  up  to  150,000  are 
employed  for  distributing  circuits.  The  variety  of  structure 
arrangements  with  electrically  operated  circuit  breakers  is 
almost  unlimited,  but  good  operating  practice  has  evolved 
certain  typical  designs  which  are  illustrated  in  the  following 
cuts  and  a  brief  discussion  will  be  given  for  each  arrangement 
shown. 

Structure  Types. — In  general  it  may  be  stated  that  there  are 
six  general  types  of  structure  arrangements  in  use: 

1.  Wall  mounting — All  apparatus  and  bus  bars  either  mounted 
directly  on  or  supported  from  a  wall  of  the  building. 

2.  Framework  mounting — All  apparatus  and  bus  bars  mounted 
on  a  framework  of  iron  pipe  or  structural  steel  shapes. 

3.  Combination  wall  or  framework  mounting. 

4.  Concrete  or  masonry  structure  mounting — all  apparatus 
mounted  in  cells. 

5.  Combination   concrete   and   structural   mounting   circuit- 
breaker  in  cells,  with  bus  bars,  etc.,  on  iron  framework. 

6.  Floor  mounting  and  structural  mounting — circuit  breakers 
set  on  floor,  with  bus  bars,  etc.,  mounted  on  iron  framework. 

Designs. — The  illustrations  show  the  use  of  the  solenoid 
operated  circuit  breakers  chiefly,  and  have  only  considered 
a  few  motor  operated  breakers.  It  will  be  noted  that  breakers  of 
relatively  small  breaking  capacity  and  of  voltages  up  to  13,200 
and  having  a  single  frame  for  all  poles  with  a  single  tank,  have 
the  solenoid  mechanisms  fastened  directly  to  the  frame  of  the 
circuit  breaker.  This  makes  the  breaker  a  more  or  less  self- 
contained  unit.  The  remaining  breakers  which  are  built  with 
each  pole  a  separate  unit  with  its  own  frame  and  tank  are  oper- 
ated from  one  solenoid  acting  on  a  common  operating  mechanism 
to  which  each  pole  is  connected. 


BREAKER  STRUCTURES 


411 


Small  6600  Volts.— Fig.  245  shows  typical  structures  for 
both  single-throw  and  double-throw  bus  systems,  with  discon- 
necting switches  on  one  side  of  the  breaker,  for  installations  for 
voltages  up  to  6600  and  of  relatively  small  capacity.  These 


FIG.  245. 


FIG.  246. 


fnoNJ  Vim 


breakers  have  the  self-contained  solenoid  mechanism  as  part  of 
the  circuit  breaker  framework. 

Small  2200  Volts. — Fig.  246  shows  the  next  size  frame  breaker 
which  has  all  poles  in  one  frame  but  separate  tanks  for  each  pole. 
This  breaker,  being  heavier,  makes  it  desirable  to  have  the  sole- 
noid mechanisms  remote  from  the  breaker,  as  shown.  This  type 


412         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

of  breaker  can  be  used  with  voltages  as  high  as  22,000  where  the 
total  station  capacity  is  small  enough  so  as  not  to  require  the 
use  of  a  cell  structure  for  the  breakers. 

6600- Volt  Cells. — The  front,  rear,  and  side  views  of  a  struc- 
ture  for   3-phase,    6600-volts,    solenoid  operated  breakers  are 


FIG.  248a. — Masonry  compartments 

for  motor  operated  breakers. 

(See  Fig.  2486  and  c.) 


FIG.  2486. 


shown  in  Fig.  247.  The  fireproof  masonry  compartment,  bus 
bars,  connections,  etc.  are  separated  by  shelves,  walls,  septums, 
etc.,  in  such  a  manner  that  no  two  conductors  of  opposite  po- 
larity are  in  the  same  compartment.  The  bus  bars  and  laminated 


BREAKER  STRUCTURES 


413 


copper  straps  are  supported  on  pillar  type  insulators  resting  on 
the  shelves  and  bent  copper  strap  forms  the  connections  from  the 
bus  bars  to  the  disconnecting  switches  and  breakers.  The  dis- 
connecting switches  are  front  connected,  mounted  on  porcelain 
pillars  attached  to  a  steel  base  located  on  the  rear  wall  of  the 
circuit-breaker  structure. 

With  the  type  of  breaker  shown  employing  solenoid  operation, 
the  leads  are  brought  out  at  the  top  of  the  breaker  tanks,  taken 
through  the  rear  walls  and  the  connections  can  then  be  run  either 
up  or  down. 


i » & 'tan  Minimum 


_&*££***? 

e 

FIQ.  248c. 

Structures  for  Motor  Operated  Breakers. — Fig.  248  shows 
typical  ways  for  arranging  bottom  connected,  motor  operated, 
13,200- volt  oil  circuit  breakers  for  connecting  to  the  bus  bars  placed 
below  them,  (A)  back  of  (B),  or  independent  of  (C)  structure 
containing  the  breakers.  A  modification  of  this  breaker  used 
particularly  when  the  leads  are  to  run  upward  has  the  connection 
brought  through  the  rear  wall  from  the  top  of  the  cylindrical  pots. 
Where  both  leads  are  to  run  upwards  the  two  pots  of  each  pole 
are  arranged  in  tandem  so  that  the  six  pots  of  a  3-pole  breaker 
are  all  in  one  continuous  line. 


414         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


BREAKER  STRUCTURES  415 

4000-Volt  Installation. — Fig.  249  shows  a  front  view,  rear 
view,  and  section  of  a  heavy  capacity  4000- volt  installation  with 
two  sets  of  bus  bars  and  a  double-throw  arangement  carried  out 
with  two  sets  of  disconnecting  switches  and  one  breaker  per  cir- 
cuit. Due  to  the  fact  that  the  bus  and  breaker  structure  had  to 
be  placed  under  an  existing  gallery  and  that  the  posts  of  the 
gallery  could  not  be  disturbed,  space  was  left  between  the  breaker 
structure  and  the  bus  structure  for  the  gallery  posts  and  this 
space  was  also  utilized  for  the  generator  and  feeder  connections. 
As  shown  on  the  rear  view,  breakers  1  and  2  were  of  1200-amperes 
capacity,  the  breakers  having  oval  tanks  and  being  guaranteed 
capable  of  rupturing  52,000  amperes  at  4500  volts.  Breaker  No. 
3  in  the  circuit  for  a  22,000-K.V.A.  generator  had  cylindrical 
tanks  20  inches  in  diameter  and  the  breaker  was  guaranteed  to 
rupture  112,000  amperes  at  4500  volts.  As  shown  in  the  sec- 
tional views  for  the  first  three  breakers,  connections  were  run  up 
in  the  opening  between  the  breaker  structure  and  the  bus  struc- 
ture to  one  of  the  breaker  terminals.  The  other  terminal  of  the 
breaker  was  connected  by  strap  passing  through  current  trans- 
formers and  two  sets  of  disconnecting  switches  either  to  the  upper 
bus  or  to  the  lower  bus.  Breaker  No.  4  was  used  for  sectionaliz- 
ing  the  lower  bus.  Breaker  No.  5  for  connecting  together  the 
upper  and  the  lower  bus,  and  breaker  No.  6  controlled  a  12,500 
K.V.A.  generator.  This  structure  has  been  considerably  ex- 
tended to  control  additional  generators  and  feeders. 

22,000-Volt  Structure.— Fig.  250  shows  a  section  thru  the 
switching  galleries  of  a  22,000-volt  installation  where  the  genera- 
tor breakers  with  their  disconnecting  switches  and  bus  bars  are 
located  on  the  second  floor  and  the  feeder  circuits,  duplicate 
busses,  and  two  sets  of  disconnecting  switches  are  located  on  the 
first  floor.  The  breakers  for  this  installation  were  guaranteed 
capable  of  rupturing  5750  amperes  at  25,000  volts. 

Influence  on  Station. — While  the  breaker  and  bus  structures 
in  certain  plants  can  be  considered  independently  of  the  balance 
of  the  equipment  in  the  station  it  is  usual  in  large  plants  to  give 
careful  consideration  to  the  effect  of  the  switch  gear  arrangement 
on  the  entire  design  of  the  station. 

In  considering  the  effect  of  the  structure  arrangement  on  the 
balance  of  the  system,  stations  may  be  considered  as  generating, 
converting,  and  transforming  stations.  In  generating  stations 
provision  has  to  be  made  for  the  generators  with  their  prime 


416         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


BREAKER  STRUCTURES 


417 


movers  and  auxiliaries  as  well  as  for  the  switching  equipment 
which  may  or  may  not  occupy  much  space.  In  converting 
stations  with  converters  or  motor-generator  sets  the  apparatus 


FIG.  250. — Masonry  compartments  for  22000  volts. 

can  usually  be  located  to  better  advantage  and  arranged  to  sim- 
plify the  wiring  and  switching  equipment.  In  transforming 
stations  where  the  bulk  of  the  power  passes  through  step  up 
or  step  down  transformers  the  switching  apparatus  can  usually 


418         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

be  so  located  with  respect  to  the  transformers  as  to  secure  the 
most  satisfactory  results.  These  transformer  stations  may  be 
indoor  or  outdoor. 

Certain  features  of  the  effect  of  circuit  breaker  and  bus  bar 
arrangement  on  the  balance  of  the  station  can  be  considered  to 
advantage  in  connection  with  a  book  on  switch  gear  in  place  of 
one  on  general  station  design. 

Locations. — In  stations  that  distribute  current  at  the  gen- 
erator voltage  there  are  three  usual  locations  for  the  oil  circuit 
breakers  and  bus  bars,  depending  principally  on  the  amount  of 
space  needed  for  this  portion  of  the  installation.  Those  loca- 
tions are  at  the  end  of  the  building,  the  sides  of  the  building,  or  in 
a  separate  switch  house. 

End  of  Building. — This  is  a  favorite  location  for  the  switch  gear 
when  the  number  of  feeders  is  such  that  this  location  provides 
sufficient  space  for  the  breakers  and  the  bus  bars,  making  due 
allowance  for  probable  future  additions.  With  this  arrangement 
it  is  customary  in  large  plants  to  provide  a  number  of  galleries  for 
the  switching  equipment.  The  switchboard  is  usually  placed 
on  one  of  the  upper  galleries  so  that  the  switchboard  operator  can 
readily  watch  the  operation  of  the  machines  which  he  is  controll- 
ing. 

Side  of  Building. — Where  the  end  of  the  building  does  not  pro- 
vide sufficient  space  the  switching  equipment  is  frequently  located 
along  one  of  the  side  walls,  usually  the  side  remote  from  the 
boiler  room,  in  a  steam  station  or  the  incoming  penstock  in  a 
hydraulic  station.  The  switching  equipment  when  arranged  in 
one  or  more  galleries  along  the  side  of  the  building  can  easily  be 
extended  as  the  space  available  for  the  switch  gear  increases 
proportionately  with  the  space  available  for  the  generating 
equipment  if  the  building  is  lengthened.  With  this  arrangement 
it  is  usually  customary  to  locate  the  generator  breakers  directly 
opposite  the  individual  machines  and  to  run  the  bus  bars  the 
length  of  the  station.  With  this  arrangement  the  length  of  the 
generator  leads  will  be  reduced  to  a  minimum  and  it  is  sometimes 
possible  to  use  bare  conductors  for  these  leads.  The  switchboard 
itself,  if  electrical  operation  is  provided,  may  be  located  either  on 
one  of  the  side  galleries  or  at  the  end  of  the  building  in  such  a 
position  that  the  switchboard  attendant  can  readily  watch  the 
operation  of  the  machine  which  he  is  controlling. 

Switch     House. — An     extension     of    this    scheme,    namely, 


BREAKER  STRUCTURES 


419 


utilizing  the  side  walls,  is  to  provide  a  separate  switch  house  and 
to  control  all  of  the  apparatus  electrically  from  a  switchboard 
in  the  main  building  or  from  a  switchboard  in  the  switch  house 
as  preferred. 

Section  of  Galleries. — Fig.  251  shows  a  section  taken 
through  the  switching  galleries  of  a  large  power  house,  and  shows 
the  arrangement  of  the  oil  circuit  breakers,  bus  bars,  series  and 


Part  SectionThrough  Feeder  Group  Switch 
and  at  the  Western  End  of  BussesTr 
Bus  Tie  Connections  and  Switch  for  Motor  T 


Section  Through  Generator  Switches 


FIG.  251. — Section  of  switching  galleries. 


shunt  transformers,  etc.  As  may  be  noted,  the  bus  bars  are 
completely  enclosed  except  for  doors  that  are  placed  opposite 
each  terminal  and  insulator,  and  in  front  of  the  disconnecting 
switches.  This  station  has  been  in  service  since  1900. 

As  shown  in  the  right-hand  portion  of  the  cut  the  generator 
circuit  breakers  are  located  on  the  top  gallery  and  the  leads  are 
brought  in  suitable  ducts  to  this  point.  The  current  trans- 
formers for  the  generator  circuit  are  located  under  a  false  floor 
and  the  leads  after  passing  through  these  transformers  go  into 


420         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

the  oil  circuit  breakers,  and  then  drop  down  through  the  floor 
to  disconnecting  switches,  and  to  the  bus  bars. 

In  addition  to  the  generator  breakers  on  the  top  gallery, 
group  breakers  are  also  installed,  while  on  the  lower  gallery  are 
located  the  feeder  breakers,  and  the  bus  tie  breakers. 

Two-phase  Station. — Fig.  252  shows  the  front  view  and  the 
section  through  the  switching  galleries  of  a  heavy  capacity  12,300- 
volt  2-phase  generating  station.  This  station  contains  the  neces- 
sary switching  equipments  for  the  control  of  8-8000-K.V.A. 
turbogenerators  and  forty  feeders  with  a  large  number  of  local 
service  circuits. 

The  connections  are  so  made  that  each  generator  feeds  through 
its  own  circuit  breaker  on  to  a  generator  bus,  which  generator 
bus  can  be  connected  through  a  second  breaker  to  two  sets  of 
group  busses,  each  group  bus  supplying  current  to  five  feeder 
circuits.  The  generator  bus  bars  are  located  directly  above  the 
breakers  in  the  upper  gallery.  The  main  bus  bars  are  the  top 
sets  on  the  middle  gallery  and  the  feeder  group  bus  bars  are  the 
lower  sets  on  the  middle  gallery. 

Ring  Bus. — The  bus  structures  are  arranged  back  to  back  in 
such  a  manner  that  the  main  bus  bars  form  one  continuous  ring 
sectioned  by  means  of  knife  switches  and  circuit  breakers  while 
the  group  bus  bars  can  be  connected  to  form  a  second  ring. 

The  bus  bars  in  this  station  consisted  of  four  copper  straps 
each  3  inches  by  ^-inch  in  section  per  phase,  these  straps 
being  supported  on  suitable  porcelain  insulators.  For  the  con- 
nections between  the  circuit  breakers,  disconnecting  switches 
and  bus  bars  copper  rod  of  suitable  size  was  used. 

With  the  arrangement  shown  in  Fig.  252,  the  disconnecting 
switches  for  isolating  the  individual  breakers  are  located  in  the 
masonry  compartments  back  of  the  breakers  so  that  it  is  practi- 
cally impossible  for  trouble  to  arise  due  to  the  station  operator 
pulling  the  wrong  disconnecting  switches  when  he  desired  to 
inspect  or  repair  a  breaker. 

Top  Connected  Breakers. — These  last  two  cuts,  namely  Figs. 
251  and  252  show  one  of  the  advantages  resulting  from  the  use 
of  top  connected  breakers  with  the  leads  brought  out  through 
the  back  wall,  namely,  the  possibility  of  locating  the  bus  bars 
between  breakers  on  two  different  galleries. 

These  may  be  considered  as  typical  arrangements — although 
old  designs  of  actual  plants — and  indicate  in  a  general  way  the 


BREAKER  STRUCTURES 


421 


422         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

space  allotted  to  this  portion  of  the  generating  station  in  plants 
of  large  capacity.  Each  installation  has  to  be  considered  on  its 
own  merits  and  the  arrangement  of  circuit  breakers  and  bus  bars 
is  a  feature  meriting  deep  study  and  careful  design. 

Synchronous  Converter  Stations. — The  proper  grouping  of  the 
apparatus  in  a  synchronous  converter  station  depends,  of  course, 
on  the  voltage  of  the  A.C.  circuit,  size  of  converter,  type  of  trans- 
formers and  similar  features  and  the  building  varies  accordingly, 
provided  the  shape  and  size  of  the  available  lot  is  such  as  not  to 
hamper  the  design  of  the  station. 


FIG.  253. — Sectional  view  of  synchronous  converter  station. 

Arrangement. — Fig.  253,  shows  the  sectional  view  of  a  syn- 
chronous converter  substation  containing  1000-K.W.  6-phase 
converters  with  air  blast  transformers  fed  from  13,200- volt  under- 
ground circuits.  As  may  be  noted  the  incoming  leads  from  the 
cable  ducts  pass  through  an  oil  breaker  and  disconnecting 
switches  to  the  bus  bars  that  are  located  on  a  gallery,  and  provi- 
sion is  made  for  an  additional  set  of  bus  bars  and  additional 
set  of  disconnecting  switches  to  be  installed  at  a  later  date  so 
that  any  breaker  may  be  connected  to  either  of  the  two  sets 
of  busses. 

The  circuit  from  these  bus  bars  passes  back  through  other 
disconnecting  switches  and  breakers  to  the  high  tension  terminals 


BREAKER  STRUCTURES  423 

located  at  the  bottom  of  the  air  blast  transformers.  The  low 
tension  leads  from  the  transformers  go  to  a  starting  panel  pro- 
vided with  double-throw  switches  that  permit  low  voltage  to  be 
impressed  on  the  converter  for  the  purpose  of  starting  and  full 
voltage  for  running.  The  converters  are  provided  with  series 
field  on  the  negative  side,  and  the  negative  and  equalizer  switches 
are  placed  on  a  pedestal  at  the  machine,  and  the  negative  and 
equalizer  busses  run  on  a  bracket  in  the  basement.  The  positive 
leads  run  to  the  panel  board  near  the  left-hand  wall  and  the  posi- 
tive bus  is  located  on  the  back  of  this  board.  The  railway 
feeders  are  run  out  through  underground  ducts  and  the  entire 
wiring  of  this  station  is  very  straight  away  from  the  high  tension 
incoming  lines  to  the  low  tension  outgoing  feeders.  All  of  the 
high  tension  A.C.  circuits  are  provided  with  electrically  operated 
breakers  controlled  from  the  main  switchboards.  The  entire 
design  of  this  station  hinges  on  the  proper  arrangement  of  the 
switching  equipment. 

M.  G.  Station. — A  similar  arrangement  of  stations  can  fre- 
quently be  utilized  to  advantage  where  motor  generators  are 
used  instead  of  converters  and  the  circuit  breakers  for  the  motors 
can  frequently  be  arranged  along  one  side  of  the  building  and  the 
corresponding  switching  equipment  for  the  generators  can  be 
placed  on  the  other  side  of  the  building  and  all  of  the  apparatus 
controlled  from  a  single  control  point.  With  such  an  arrangement 
the  wiring  is  kept  very  straight  and  simple  and  the  space  is 
utilized  to  the  best  advantage. 

Portable  Substation  for  Converter. — Many  interurban  electric 
railways  have  portable  substations  located  in  freight  cars  and 
arranged  for  ready  transportation  to  whatever  point  requires 
their  temporary  service.  Fig.  254  shows  a  typical  installation 
of  this  kind  with  a  500-K.W.  6-phase  converter,  2—250- 
K.V.A.  oil  insulated  self-cooling  transformers  and  the  necessary 
panel  switchboard,  high  tension  oil  circuit-breaker  and  lightning 
protective  devices  in  the  33,000-volt  circuit.  The  general 
arrangement  of  the  apparatus,  method  of  wiring  and  other  details 
are  clearly  shown  in  the  cut.  The  operator  standing  in  the 
middle  of  the  car  is  convenient  to  the  commutator  end  of  the 
rotary  converter. 

Portable  Substation  for  M.  G.  Set. — Fig.  255  shows  a 
similar  portable  substation  supplied  to  Brazil  and  containing  a 
50-cycle,  6600-volt,  3-phase  synchronous  motor  direct  connected, 


424         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


BREAKER  STRUCTURES 


425 


to  a  D.C.  generator.  The  switchboard  is  provided  with  a  panel 
for  the  self-starting  synchronous  motor  with  its  exciter,  a  panel 
for  the  D.C.  generator  and  2-D.C.  feeder  panels.  The  difference 
in  the  type  of  car  used  is  as  noticeable  as  the  difference  in  the 
arrangement  of  the  apparatus  which  they  contain. 


Section  B-B 

Section  A- A 
FIG.  255. — Portable  substation  for  motor  generator. 

While  the  entire  trend  of  American  design  during  recent  years 
has  been  to  locate  transformers  and  high  tension  switch  gear  out 
of  doors,  there  are  a  few  cases  where,  due  to  local  conditions, 
indoor  equipment  is  utilized. 

Comparison  Indoor  and  Outdoor. — For  this  reason,  and  to 
permit  a  direct  comparison  between  high  tension  indoor  and 
outdoor  arrangements,  a  number  of  drawings  have  been  selected 


426         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


BREAKER  STRUCTURES 


427 


mostly  of  older  design,  showing  the  arrangement  of  hydro- 
electric generating  stations  for  various  voltages  from  44-K.V. 
up  to  110-K.V. 

INDOOR  STATIONS 

44-K.V.  Indoor.— Fig.  256  shows  the  plan  view  and  Fig.  257 
shows  the  sectional  views  of  a  generating  station  containing 
5 — 1875  K.V.A.  3-phase  horizontal  shaft  generators,  5  banks 
each  of  3— 625-K.V.A.  2300  to  44-K.V.  step  up  transformers 
two  44-K.V.  outgoing  transmission  lines  and  two  water  wheel 
driven  exciters. 

A  panel  switchboard  was  provided  with  electrically  operated 
breakers  in  the  L.  T.  and  H.  T.  circuits. 


FIG.  257. — Sectional  views  44-K.V.  station. 

The  leads  are  taken  from  the  generator  as  under  ground  cables 
to  the  L.  T.  switch  gear.  Each  generator  with  its  bank  of  trans- 
formers was  provided  with  3 — electrically  operated  breakers 
so  that  the  generator  could  be  normally  connected  directly  to 
its  own  transformer  bank,  or  either  generator  or  transformer 
could  be  connected  to  the  transfer  bus. 

The  transformer  low  tension  delta  bus  is  supported  in  the 
framework  carrying  the  low  tension  breakers  with  their  discon- 
nects. From  the  high  tension  side  of  the  transformers  leads  are 
taken  through  an  oil  breaker  and  disconnecting  switches  to 
a  44-K.V.  bus,  this  bus  being  hung  from  a  series  of  suspension 
insulators  that  are  stretched  between  the  roof  girders  and  the 
steel  work  that  carries  the  disconnecting  switches  above  the 
44-K.V.  breakers. 


428         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


BREAKER  STRUCTURES 


429 


430         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

From  this  bus,  connections  are  taken  through  disconnecting 
switches,  breakers,  disconnecting  switches  and  choke  coils  to 
the  line  outlet  bushings  set  in  the  side  wall.  The  electrolytic 
arresters  are  of  the  usual  type  located  out  of  doors.  The  par- 
ticular designs  shown  in  Figs.  256  and  257  were  prepared  in 
December,  1909. 

55-K.V.  Indoor. — Figs.  258  and  259  show  the  plan  views  and 
sections  of  a  55-K.V.  station  whose  designs  were  prepared  in 
December,  1909.  This  station  contains  six  5400-K.V.A.  12-K.V. 
3-phase  generators,  five  banks  each  of  three  1800-K.V.A. 
transformers,  12  K.V.  to  32  K.V.,  delta  connection  low  tension, 
star  connection  high  tension  for  55-K.V.  service;  two  55-K.V. 
feeders,  two  12-K.V.  feeders,  one  water  wheel  driven  exciter, 
300  K.W.  250  volts,  one  similar  exciter  that  can  be  coupled 
either  to  a  water  wheel  or  to  a  motor;  the  motor  being  arranged 
for  coupling  to  either  exciter. 

Provision  was  made  for  grounding  the  neutral  of  the  generators 
by  means  of  disconnecting  switches  to  a  neutral  bus  and  this  in 
turn  connecting  through  a  grounding  resistor. 

All  of  the  12-K.V.  breakers  are  located  in  a  gallery  above  the 
compartment  containing  the  transformers  and  high  tension 
switching  equipment.  The  generator  leads  are  carried  up  the 
columns  that  support  the  gallery  and  pass  through  the  oil 
breakers  to  a  main  bus,  or  an  auxiliary  bus,  and  thence  back  to 
the  low  tension  side  of  the  transformers.  The  high  tension  leads 
from  the  transformers  pass  through  oil  breakers  and  disconnect- 
ing switches  to  a  55-K.V.  bus  that  is  hung  from  suspension  insu- 
lators. From  that  bus  connections  are  taken  through  discon- 
necting switches,  oil  breakers,  other  disconnecting  switches  and 
choke  coils  to  the  line  outlet  bushings. 

The  12-K.V.  and  55-K.V.  lightning  arresters  are  arranged  for 
outdoor  service. 

The  generators  and  main  A.C.  connections  are  controlled  from 
a  desk  while  the  exciter  and  field  circuits  are  operated  electri- 
cally from  the  desk  by  means  of  breakers  located  on  the  exciter 
and  field  panels. 

110-K.V.  Indoor. — Fig.  260  shows  the  arrangement  of  a  100 
K.V.  generating  station  using  3-phase  transformers. 

This  plant  contains  two  450-H.P.  horizontal  shaft  water 
wheels,  each  driving  a  300-K.W.  250-volt  exciter,  and  six  9700 
H.P.  horizontal  shaft  water  wheels,  each  driving  a  7800-K.V.A. 


BREAKER  STRUCTURES 


431 


432         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

4-K.V.,  3-phase  generator,  and  six  7800-K.V.A.  3-phase  trans- 
formers, 110K.V. 

In  this  plant  it  was  the  intention  that  the  generators  should 
draw  air  in  around  the  shaft  and  discharge  it  at  the  bottom  of 


the  stator  to  a  short  duct  connecting  with  the  tailrace.  With 
this  arrangment  of  discharging  the  heated  air  from  the  genera- 
tors into  the  tailrace  and  locating  the  field  rheostat  resistors 


BREAKER  STRUCTURES  433 

of  the  generator,  outside  the  building  as  is  sometimes  done,  the 
question  of  ventilation  is  considerably  simplified. 

The  leads  from  the  generators  are  carried  to  the  low  tension 
breaker  and  bus  structure,  thence  to  the  low  tension  side  of  the 
transformers  and  from  the  high  tension  side  through  breakers 
to  the  high  tension  busses. 

Alternative  arrangements  have  been  indicated  locating  the 
lightning  arrester  tanks  indoor  and  outdoor. 

This  station  was  designed  in  March,  1911. 

Spanish  Stations  110-K.V. — Fig.  261  shows  a  sectional  view 
through  the  110-K.V.  station  at  the  Seros  plant  of  the  Ebro 
Irrigation  &  Power  Company  in  Spain,  this  being  the  first  in- 
stallation in  Europe  to  operate  at  a  voltage  above  100  K.V. 

The  plant  contains  four  14,500-H.P.  vertical  shaft  water 
wheels  with  provision  for  a  fifth,  four  8000-K.W.  50-cycle, 
6600-volt,  13,300-KV.A.  generators,  with  provision  for  a  fifth, 
and  four  banks  of  4444-K.V.A.  50-cycle  single  phase  transformers 
stepping  up  to  110  K.V.  for  transmission  to  Barcelona.  Plant 
was  installed  about  1911. 

Fig.  262  shows  the  arrangement  of  the  Tremp  plant  of  the 
same  system  installed  about  1913.  This  plant  contains  four 
12,500-H.P.  horizontal  shaft  twin  turbines  driving  8750-K.W. 
14,500-K.V.A.  3-phase  generators,  having  transformers  with 
transmission  lines  at  110-K.V.  to  Barcelona  and  25-K.V.  from 
Pobla. 

The  operating  gallery  is  arranged  to  overlook  the  generator 
room  and  the  relay  and  recording  instruments  are  mounted 
on  panels  back  of  the  control  desk.  Back  of  the  relay  board  are 
the  low  tension  6-K.V.  circuit  breakers  with  their  bus  bars  and 
connections. 

The  high  tension  leads  from  the  transformers  are  taken  up 
through  a  floor  opening  to  high  tension  breakers  and  then  through 
disconnects  to  the  high  tension  bus.  Connections  are  taken 
from  that  bus  to  disconnecting  switches  and  breakers,  and  thence 
out  to  the  transmission  line,  the  arresters  being  located  on  the 
roof  of  the  building. 

The  high  tension  breakers  in  both  of  these  Ebro  plants  have  the 
tandem  arrangement  of  tanks  so  that  all  six  terminals  of  the 
3-pole  breakers  come  in  one  plane. 

Montana  Power. — Fig.  263  shows  a  sectional  view  through 
the  Holter  plant  of  the  Montana  Power  Company,  this  plant  hav- 

28 


434         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


BREAKER  STRUCTURES 


435 


ing  been  installed  about  1916.  The  plant  contains  four 
16,000-H.P.  vertical  shaft  water  wheels  with  12,000-K.V.A. 
6600-volt  generators  and  four  3-phase  transformers  with  a 
normal  rating  of  12,000  K.V.A.  each,  maximum  rating  of  16,000 
K.V.A. 


FIG.  263. — Sectional  view  Holier  Plant,  110  K.V. 

The  leads  from  the  generators  are  taken  through  the  breakers 
to  the  6600-volt  main  bus,  back  from  that  bus  through  similar 
breakers,  or  from  the  cross  connection  bus  directly  from  the 
generators  to  the  low  tension  side  of  the  step  up  transformers. 

The  leads  from  the  high  tension  side  of  the  transformers  are 
taken  up  through  floor  openings  where  they  are  attached  between 


436         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

insulators  and  thence  through  choke  coils  and  disconnecting 
switches  to  the  high  tension  breakers,  then  to  the  bus  and  from 
the  bus  back  to  other  disconnecting  switches,  breakers  and  dis- 
connects through  roof  outlet  bushings. 

A  grounding  switch  is  located  near  these  roof  outlet  bushings 
for  grounding  the  high  tension  circuit,  and  the  electrolytic 
lightning  arresters  are  located  on  the  roof  of  the  building. 


Roof  Bush  I  fry 


FIG.  264. — Transverse  section.     General  Station,  Inawashiro  Hydro 
Electric  Power  Co. 

Inawashiro. — Fig.  264  shows  a  transverse  section  through  a 
portion  of  generating  station  of  the  Inawashiro  Hydro  Electric 
Power  Company  of  Japan.  This  plant  installed  about  1915 
contains  6-7700-K.V.A.  6-K.V.,  3-phase  generators,  12-4400 
K.V.A.  single  phase  transformers  and  two  outgoing  115-K.V. 
transmission  lines  Power  is  transmitted  a  distance  of  145  miles 
to  Tokio  where  there  is  a  receiving  station  whose  original  equip- 
ment included  12-4000-K.V.A.  transformers  stepping  down  to 
11  K.V.  for  underground  distribution. 

Fig.  264  shows  a  transverse  section  through  the  portion  of 
the  building  devoted  to  the  transformers  and  the  switching 
equipments.  The  incoming  penstock  to  the  water  wheel  passes 


BREAKER  STRUCTURES  437 

under  this  portion  of  the  building  and  the  warm  air  passing 
from  the  generators  is  so  arranged  that  it  can  discharge  air  into 
the  switching  galleries  if  needed  there  during  cold  weather  or  it 
can  be  discharged  in  such  a  way  as  to  warm  the  lightning  arrester 
equipment  which  is  located  out  of  doors. 

The  transformers  are  placed  in  masonry  compartments  and 
are  so  arranged  that  they  can  be  pulled  out  into  the  power 
house  where  they  can  readily  be  lifted  out  by  the  crane  which 
spans  the  generator  room.  The  piping  and  valves  for  the  water- 
cooled  transformers  are  so  arranged  that  they  can  readily  be 
disconnected  so  that  any  transformer  can  be  pulled  out  of  the 
compartment  into  the  generator  room  at  the  floor  level  so  that 
it  can  be  handled  to  advantage  by  the  crane. 

The  relative  location  of  the  oil  circuit  breakers  and  bus  bars 
in  the  6600-volt  circuit  as  well  as  the  oil  circuit  breakers,  discon- 
necting switches,bus  bars  and  similar  devices  in  the  115-K.V. 
circuit  is  evident. 

Path  of  Current. — As  may  be  noted  from  this  drawing  the  cur- 
rent passes  from  the  lower  bus  through  the  disconnecting  switches 
into  the  oil  circuit  breaker,  out  through  other  disconnecting 
switches  and  current  transformers  to  the  cables  carrying  the 
current  to  the  low  tension  side  of  the  step  up  transformer.  The 
high  tension  side  of  the  step  up  transformer  connections  are  taken 
to  the  high  tension  delta  bus  and  the  leads  are  then  carried  up 
through  the  floor  by  means  of  copper  tubing.  This  copper  tub- 
ing is  mounted  on  the  high  tension  wiring  support.  These  con- 
nections then  pass  into  the  high  tension  breaker  and  through 
disconnecting  switches  to  the  high  tension  bus.  Coming  back 
from  the  high  tension  bus  the  current  passes  through  disconnect- 
ing switches  into  the  breaker,  then  from  the  breaker  through 
other  disconnecting  switches  to  the  line  outlet  bushing  where 
the  leads  are  taken  through  the  roof  and  are  then  taken  through 
the  choke  coils  to  the  outgoing  line  circuit.  The  lightning  arrest- 
ers located  outside  the  building  are  attached  to  the  transmission 
lines  outside  of  the  choke  coils. 

The  supports  for  the  bus  bars  and  wiring  in  the  115-K.V. 
circuit  were  made  up  of  a  number  of  insulators  built  into  columns 
corresponding  to  the  columns  used  on  the  disconnecting  switches. 
These  wiring  supports  were  made  of  the  rigid  type  instead  of 
suspension  insulators,  to  prevent  any  vibration  that  might  be 
caused  by  earthquakes  in  the  neighborhood  of  the  station. 


438         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

The  115-K.V.  bus  bars,  wiring,  and  connections  are  made  of 
copper  tubing,  %-inch  gas  pipe  size  having  a  nominal  outside 
diameter  of  1.04  and  a  nominal  inside  diameter  of  .78  inches. 

This  set  of  illustrations  suggests  various  ways  of  arranging 
hydroelectric  plants  and  locating  transformers  and  high  tension 
apparatus  indoors.  The  portion  of  the  building  devoted  to 
transformers  and  high  tension  switch  gear  can  be  readily  de- 
termined and  the  expense  of  such  portions  of  the  building  should 
be  charged  against  the  indoor  installation  when  a  comparison  is 
being  made  between  indoor  and  outdoor  equipment. 

In  most  cases  it  will  be  found  that  a  considerably  cheaper  and 
better  arrangement  can  be  made  by  locating  the  transformers 
and  switch  gear  out  of  doors. 

A  direct  comparison  between  indoor  and  outdoor  designs  for 
154-K.V.  service  is  given  later. 

OUTDOOR  STATIONS 

While  the  arrangement  of  any  outdoor  station  has  to  be  deter- 
mined from  local  conditions  and  the  circuits  to  be  controlled,  a 
series  of  typical  layouts  have  been  prepared  to  show  suggested 
arrangements  for  various  voltages. 

In  order  to  cover  as  many  different  classes  of  arrangements  as 
practicable,  certain  figures  show  single  phase  transformers  and 
others  three  phase,  some  figures  have  water-cooled  units,  others 
self-cooling  radiator  type.  Various  features  that  appear  on  one 
figure  can  be  utilized  to  advantage  with  the  arrangement  indi- 
cated on  others. 

22-K.V.  Outdoor. — Fig.  265  shows  a  22-K. V.  transformer  and 
switching  station,  for  the  control  of  2-5000  K. V.A.  and  4-10,000 
K.V.A.  3-phase  transformers  feeding  out  over  four  15,000 
K.V.A.  22-K.V.  transmission  lines. 

This  station  is  arranged  so  that  the  high  tension  bus  can  be 
sectioned  in  the  middle,  one  5000-K.V.A.  and  2-10,000-K.V.A. 
feeders  being  connected  to  each  section.  The  sectionalizing  of 
the  bus  permits  shutting  down  half  of  it  at  a  time  for  inspection, 
cleaning  and  repairs.  By  making  the  bus  tie  breaker  automatic 
with  instantaneous  tripping  under  short-circuit  conditions  and 
providing  the  other  breakers  with  definite  time  limit  relays, 
arrangements  can  be  made  so  that  only  half  the  station  capacity 
will  be  concentrated  on  a  short  circuit. 


BREAKER  STRUCTURES 


439 


440         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

Path  of  Current. — The  incoming  low  tension  circuits  to  the 
various  transformers  are  controlled  by  suitable  breakers  in  a  low 
tension  switch  house  adjacent  to  the  high  tension  outdoor  in- 
stallation. The  leads  from  the  switch  house  are  brought  as 
underground  cables  in  a  tunnel  to  a  point  near  the  transformers 
and  then  brought  up  to  suitable  potheads  supported  independ- 
ently of  the  transformer  tanks. 

The  high  tension  transformer  leads  pass  through  disconnecting 
switches  into  an  electrically  operated  oil  breaker  and  pass  out 
through  a  second  set  of  disconnecting  switches  to  the  22-K.V.  bus. 
The  circuit  passes  through  disconnecting  switches  to  the  line 
breaker  and  through  a  second  set  of  disconnecting  switches  and 
choke  coils  to  the  outgoing  circuit,  22-K.V.  lightning  arresters 
are  tapped  off  these  outgoing  lines.  Disconnecting  switches  on 
each  side  of  each  high  tension  breaker  facilitate  the  safe  inspec- 
tion of  the  breaker.  Typical  structural  steel  framework  is 
indicated  for  the  support  of  the  disconnecting  switches  and  busses. 
The  arrangement  of  the  steel  work  and  the  supporting  towers  is 
diagrammatic,  no  attempt  having  been  made  to  figure  the  exact 
design  of  the  various  members. 

While  the  high  tension  breakers  are  used  in  a  22-K.V.  circuit 
the  illustration  has  been  prepared  on  the  basis  of  utilizing  37- 
K.V.  breakers  to  secure  ample  rupturing  capacity  for  a  60,000- 
K.  V.A.  plant.  25-K.  V.  breakers  would  be  slightly  smaller  than  those 
indicated  in  this  figure,  while  50-K.V.  breakers  would  be  slightly 
larger,  but  the  general  appearance  of  a  33  or  44-K.V.  transformer 
and  switching  station  would  correspond  closely  with  Fig.  265. 

66-K.V.  Outdoor.— Fig.  266  shows  a  typical  66-K.V.  trans- 
former and  switching  station  used  with  two  banks  each  of  3- 
2000-K.V.A.,  0. 1.  S.  C.  radiator  type  transformers,  with  one  spare 
transformer.  This  equipment  is  located  immediately  outside  of 
a  steam  generating  station  and  the  low  tension  leads  to  the 
transformer  banks  are  brought  as  lead-covered  cable  underground 
and  up  the  outside  of  the  building.  The  low  tension  delta  is 
made  at  the  transformers  and  a  single  bracket  attached  to  the 
side  wall  is  arranged  to  carry  the  insulators  for  the  66-K.V.  delta 
connection  as  well  as  the  insulator  for  the  13.2-K. V.  delta  connec- 
tion. 

Each  transformer  is  on  wheels,  arranged  so  that  it  can  be 
readily  rolled  onto  a  truck  and  the  spare  transformer  pushed  into 
its  position.  No  provision  is  made  by  means  of  double-throw 


BREAKER  STRUCTURES 


441 


disconnecting  switches  to  cut  in  the  spare  transformer  in  place 
of  any  other  transformer. 

Each  transformer  bank  is  supplied  with  one  electrically  operated 
frame   mounted   oil   breaker   connected   through  disconnecting 


V-V  NOI103S 


switches  to  a  66-K.V.  bus  sectioned  in  the  middle.  This  66-K.  V. 
bus  in  turn  supplies  a  total  of  4-66-K.  V.  outgoing  feeders  through 
disconnecting  switches  and  oil  breakers.  Line  suspension  choke 
coils  are  connected  into  the  outgoing  feeder  circuits  and  electro- 
lytic lightning  arresters  are  tapped  off  of  these  circuits.  The  oil 


442         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

circuits  breakers  indicated  on  this  drawing  are  the  400-ampere, 
73-K.V.  frame  mounted  breakers.  This  layout  is  based  on  that 
of  an  installation  in  the  Middle  West. 

88-K.V.  Outdoor.— Fig.  267  shows  a  typical  88-K.V.  outdoor 
switching  equipment  used  in  connection  with  two  7000-K.V.A.  3 
phase,  oil  insulated,  self-cooled  radiator  type  transformers. 
There  are  two  high  tension  incoming  lines  connecting  through 


FIG.  267. — 88  K.V.  outdoor  switching  station. 

disconnecting  switches  and  oil  breakers  to  a  high  tension  bus, 
sectioned  in  the  middle  by  means  of  a  breaker.  Each  section  of 
bus  connects  in  turn  by  disconnecting  switches  and  a  breaker  to 
the  high  tension  side  of  a  7000-K.V.A.  transformer. 

The  6.6-K. V.  side  of  each  transformer  connects  through  discon- 
necting switches  and  oil  breakers  to  a  low  tension  bus  that  is  also 
sectioned  in  the  middle.  This  6.6.-K.  V.  low  tension  bus  supplies 
current  to  four  6.6-K.V.  outgoing  feeder  circuits.  For  this 
installation  the  low  tension  breakers  and  busses  as  well  as  the 


BREAKER  STRUCTURES 


443 


high  tension  breakers  and  busses  have  been  shown  as  being  of  the 
outdoor  type. 

The  oil  circuit  breakers  indicated  for  use  in  the  88-K.V.  cir- 
cuits, are  the  400-amperes,  95-K.V.  breakers. 

The  disconnecting  switches  in  the  88-K.V.  circuits  are  of  the 
normal  inverted  single-pole  type  to  be  operated  from  the  ground 
by  means  of  a  long  pole. 

110-K.V.  Outdoor. — Fig.  268  shows  in  plan  view,  a  typical 
110-K.V.  outdoor  transforming  station  used  for  the  control  of 


FIG.  268. — Plan  view  110  K.V.  outdoor  station. 

4 — 110-K.V.  transmission  line  circuits  and  six  banks  of  trans- 
formers, each  of  3 — 5000-K.V.A.,  O.  I.  S.  C.  radiator  type  units. 
The  arrangement  shown  is  a  slight  modification  of  an  actual 
installation  that  has  been  operating  in  the  South  for  a  number  of 
years,  and  the  location  and  type  of  disconnecting  switches 
corresponds  with  those  in  service. 

For  this  station  all  of  the  low  tension  switching  is  controlled 
by  means  of  breakers  located  in  a  low  tension  switch  house 
adjacent  to  the  high  tension  transformer  yard. 

Section. — The  high  tension  leads  from  each  transformer,  as 
shown  in  Fig.  269,  are  taken  through  disconnecting  switches  to 
a  115-K.V.  round  tank  oil  breaker.  The  leads  from  the  trans- 
former oil  breakers  then  pass  through  other  disconnecting 


444         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

switches  to  the  110-K.V.  bus  at  the  same  time  tapping  across 
to  the  disconnecting  switches  and  breakers  for  the  outgoing 
line  circuits. 

The  two  sets  of  110-K.V.  bus  bars,  one  on  each  side  of  the 
railway  transfer  track  can  be  connected  by  means  of  the  oil 
breaker  in  the  outer  row  at  the  right  center  as  shown  by  section 
B.B. 

This  installation  contemplates  4 — 110-K.V.  line  circuits  and 
to  reduce  the  cost  of  the  arrester  equipment  each  pair  of  lines, 


To  low  Tension  Switch  House 


To  low  Tension  Snitch  Hov 

Section    BB 
FIG.  269. — Section  view  110  K.V.  outdoor  station. 


which  normally  operate  in  parallel  is  provided  with  two  sets 
of  horn  gaps,  but  only  one  set  of  arrester  tanks  with  their  oil, 
trays  and  electrolyte. 

Disconnecting  switches  of  the  inverted  single-pole  type,  pole 
operated,  or  of  the  inverted  or  upright,  multiple  pole,  mechanic- 
ally operated  type  can  be  substituted,  if  desired  in  place  of 
those  shown,  and  would  usually  be  considered  preferable,  owing 
to  the  inherent  weakness  of  a  long  heavy  porcelain  column  in  a 
position  of  a  practically  horizontal  cantilever  beam. 

132-K.V.  Outdoor. — Fig.  270,  shows  in  plan  view,  a  typical 
132,-K.V.  transformer  and  switching  station.  In  this  station, 
there  are  two  banks,  each  of  3— 10,000-K.V.A.,  single-phase 


BREAKER  STRUCTURES 


445 


transformers,  11-K.V.  low  tension  voltage,  132-K.V.  high  tension 
voltage  with  2 — 132-K.V.  outgoing  transmission  lines  running  up 
the  side  of  the  hill.  This  arrangement  is  based  on  the  Windsor 
installation  of  the  West  Penn  Power  Company. 

In  this  installation,  the  low  tension  leads  are  brought  from  the 
adjacent  steam  generating  station  in  a  cable  tunnel  to  the  trans- 
formers. The  high  tension  transformer  leads  are  carried  over 
head  between  strain  insulators  and  taps  are  taken  down  from 


Fio.  270. — 132  K.V.  outdoor  switching  station. 

these  cross  connections  to  the  breakers  and  the  current  passes 
through  disconnecting  switches  and  breakers  to  the  transmission 
line  or  can  feed  back  through  other  disconnecting  switches  and 
breakers  to  a  high  tension  transfer  bus. 

Provision  is  actually  made  in  this  plant  for  tieing  together  this 
transformer  yard  feeding  one  distributing  system  with  its  two 
30,000-K.V.A.  transformer  banks  to  another  transformer  yard 
of  slightly  larger  capacity  feeding  a  different  transmission 
system. 

The  disconnecting  switches  used  for  isolating  the  oil  breakers 
are  of  the  inverted  type  for  pole  operation.  On  the  outgoing 


446         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

line  breakers,  a  combination  choke  coil  and  single-pole  discon- 
necting switch  is  utilized.  As  part  of  the  lightning  arrester 
equipment,  mechanically  operated  3-pole  rotating  type, 
double-break  disconnecting  switches  with  an  auxiliary  grounding 
device  is  furnished.  Mechanically  operated  3-pole  disconnecting 
switches  are  usually  preferable  to  any  other  type  for  voltages 
higher  than  88  K.V.  in  so  far  as  operation  is  concerned,  but  they 
normally  require  more  elaborate  steel  structures  to  permit  their 
satisfactory  use. 

Comparison  Indoor  and  Outdoor. — To  give  a  concrete  com- 
parison of  transformer  and  switching  stations  for  indoor  and 
outdoor  service  at  110  K.V.  and  154  K.V.  Fig.  271  and  Fig. 
272  have  been  prepared  to  show  typical  arrangements  in  a  large 
capacity  water  power  plant  to  contain  6 — 22,500-K.V.A.  genera- 
tors, 6  banks  each  of  3 — 7500-K.V.A.  single-phase  step  up  trans- 
formers and  4 — 45,000-K.V.A.  transmission  lines.  The  portion 
of  the  building  intended  for  the  generators  has  been  drawn  up  for 
both  horizontal  and  vertical  shaft  units. 

Indoors. — Fig.  271,  shows  the  generating  station  with  indoor 
transformers.  On  this  drawing  Fig.  1  shows  a  sectional  view 
through  the  transformer  and  switch  building  to  show  the  general 
location  proposed  for  the  transformers,  oil  circuit  breakers, 
disconnectings  switches,  bus  bars,  lightning  arresters  and  other 
apparatus.  This  portion  of  the  drawing  as  well  as  the  balance 
of  the  drawing  has  been  made  to  scale  showing  the  devices  needed 
for  the  154-K.V.  installation.  Two  sets  of  dimensions  have  been 
marked  in  certain  places,  one  giving  the  overall  dimensions  for 
154-K.V.  service,  the  other  for  110-K.V.  service. 

Section. — As  shown  in  the  sectional  view,  Fig.  2,  the  11-K.V. 
oil  circuit  breakers  and  bus  bars  are  located  back  of  the  trans- 
formers, transformers  being  on  wheels  to  permit  their  being 
readily  rolled  out  into  the  generating  station  where  they  can  be 
handled  by  the  overhead  crane. 

The  high  tension  leads  from  the  transformers  are  taken  up 
through  floor  openings  and  are  mounted  on  suitable  supports. 
These  supports,  as  well  as  the  piller  supports  for  the  disconnect- 
ing switches  for  indoor  service,  will  probably  be  made  of  micarta 
tubing  although  possibly  porcelain  insulators  built  up  in  suitable 
columns  may  be  employed. 

The  high  tension  neutral  is  run  in  the  same  compartment  as 
the  transformers. 


BREAKER  STRUCTURES 


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448         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

The  phase  leads  from  the  transformers  after  passing  up  through 
the  floor  openings  go  into  the  oil  circuit  breaker.  From  the  oil 
circuit  breaker  they  are  taken  through  either  of  the  sets  of  dis- 
connecting switches  to  either  of  the  two  high  tension  busses. 
These  high  tension  busses  are  suspended  from  the  roof  trusses 
in  the  manner  indicated.  These  bus  supports  will  probably  be 
of  the  suspension  insulator  type  although  they  may  be  a  rigid 
built-up  porcelain  column,  or  possibly  micarta  tubing  supports 
will  be  utilized. 

From  the  busses  the  leads  are  taken  back  through  the  discon- 
necting switches  through  the  oil  circuit  breaker,  then  to  the  line 
disconnecting  switch,  the  roof  bushing,  choke  coils,  and  thence 
to  the  high  tension  line. 

The  lightning  arresters  with  their  horn  gaps,  transfer  switches 
and  arrester  tanks  are  located  on  the  roof  of  the  building. 

Section  at  Centre. — On  this  same  drawing,  Fig.  2  is  a  section 
taken  at  the  center  of  the  building  to  show  the  location  of  the 
bus  junction  oil  circuit  breakers  on  the  high  tension  gallery,  the 
control  desk,  local  service  board  and  battery  room  on  the  mez- 
zanine gallery,  the  field  and  exciter  board  and  rheostat  resistors 
on  the  lower  floor. 

Space  Requirements. — A  space  the  entire  length  of  the  generat- 
ing station  320  feet  long,  has  been  allotted  to  the  transformers 
and  switching  equipment. 

For  the  154-K.V.  arrangement  this  portion  of  the  building 
will  have  a  height  of  76  feet  and  a  width  of  44  feet,  allowing  about 
6  feet  between  phases  and  4  feet  to  ground. 

For  the  110-K.V.  proposition  allowing  5  feet  between  phases, 
3  feet  to  ground,  the  portion  of  the  building  devoted  to  trans- 
former and  switching  equipment  would  have  a  height  of  64  feet 
and  a  width  of  36  feet. 

Plan  H.T.  Room. — Fig.  3  shows  a  plan  view  of  the  high  ten- 
sion switching  room.  As  may  be  noted,  the  high  tension  oil 
circuit  breakers  are  arranged  in  a  row  near  the  wall  between  the 
transformer  house  and  the  generator  house,  while  the  bus  bars 
have  beeen  shifted  slightly  towards  the  outside  wall  of  the 
building. 

Space  has  been  left  available  so  that  if  desired  breakers  and 
disconnecting  switches  for  two  additional  lines  can  be  readily 
installed,  one  at  the  extreme  right  hand  and  one  at  the  extreme 
left-hand  end. 


BREAKER  STRUCTURES  449 

The  tie  breakers  as  well  as  the  bus  junction  breakers  are  located 
near  the  central  portion  of  the  high  tension  switch  room. 

The  high  tension  bus  bars  in  addition  to  being  suspended  from 
the  roof  trusses  as  shown  in  the  sectional  view  are  held  by  strain 
insulators  at  each  end  of  the  building  to  minimize  vibration. 

Plan  Main  Floor. — Fig.  4  on  this  same  drawing  shows  the  plan 
view  of  the  main  floor  of  the  power  house  using  horizontal  shaft 
water  wheel  generators  and  making  the  transformer  house  inte- 
gral with  the  generating  station.  A  note  is  placed  on  this  Fig.  4 
showing  the  location  of  the  station  wall  if  outdoor  transformer 
and  switch  yard  is  used. 

The  various  transformers  have  been  indicated  as  being  in 
transformer  compartments,  so  arranged  that  any  one  trans- 
former can  be  readily  rolled  out  on  its  wheels  to  a  point  where  it 
may  be  lifted  by  the  traveling  crane. 

Outdoor  Layout. — Fig.  272  shows  outdoor  transformer  and 
switch  yard.  This  drawing  which  has  been  made  to  scale  show- 
ing the  154-K.V.  installation  has,  in  most  places,  two  sets  of 
dimensions,  one  giving  the  dimensions  for  the  154-K.V.  installa- 
tion, and  the  other  for  the  corresponding  110-K.V.  installation. 

Plan  View. — The  bottom  portion  of  the  drawing  shows  the  plan 
view  location,  the  transformer  bank,  the  four  outgoing  lines,  the 
bus  tie  and  junction  circuits  and  similar  main  features. 

Longitudinal  Elevation.  —  On  this  plan  view  a  center  line  marked 
'EEE'  has  been  placed  to  show  where  the  longitudinal  eleva- 
tion has  been  taken.  This  longitudinal  elevation  has  been  taken 
in  such  a  manner  as  to  show  most  of  the  important  features, 
such  as  the  horn  gaps,  the  arrester  tanks,  the  transformer  banks 
with  their  neutral  connections  and  neutral  busses,  the  transformer 
oil  breaker,  the  framework  and  supports  for  the  selector  type 
switches  in  the  transformer  and  line  circuits,  the  junction  breaker, 
tie  breaker,  etc. 

Line  Equipment. — On  the  upper  portion  of  the  drawing,  sec- 
tion 'A A'  shows  the  line  equipment.  As  may  be  noted,  con- 
nections are  taken  from  the  bus  bars  to  short  leads  that  are 
stretched  between  strain  insulators  attached  to  the  lower  frame- 
work and  to  the  supporting  framework  of  the  selector  switches. 
The  leads  pass  thence  to  the  outside  studs  of  the  selector  switches 
and  from  the  central  studs  to  the  wires  that  are  held  by  the 
strain  insulators  attached  to  the  tower  structure.  From  these 
wires,  the  leads  drop  to  the  line  breaker  and  from  the  line  breaker 


450         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


BREAKER  STRUCTURES  451 

to  the  line  disconnecting  switch  and  choke  coils,  to  the  outgoing 
line  circuit.  The  horn  gaps,  transfer  switch  and  arrester  tanks 
of  the  arrester  appear  on  this  sectional  view. 

Transformer  Equipment. — Section  at  'BB'  shows  the  trans- 
former equipment  and  shows  how  the  high  tension  lead  passes 
from  the  transformer  to  the  oil  breaker,  from  the  oil  breaker  to 
the  wire  that  is  stretched  across  the  strain  insulators  attached 
to  the  tower  framing.  From  this  wire  the  leads  pass  to  the 
central  stud  of  the  double-throw  disconnecting  switch.  The 
outer  studs  of  these  switches  are  connected  up  to  the  busses  in 
the  manner  shown. 

Bus  Connection. — Section  at  'CC'  shows  the  bus  cross  con- 
nections while  section  at  'DD'  shows  the  bus  tie  arrangement. 

Neutral  Resistor. — With  the  outdoor  equipment  as  shown  on 
Fig.  272  the  neutral  grounding  resistors  will  have  to  be  housed  in 
as  they  are  not  suitable  for  exposure  to  the  weather  The  en- 
closure for  the  grounding  resistor  is  made  a  portion  of  the  central 
tower,  and  a  suitable  roof  bushing  is  furnished  for  taking  in  the 
leads  from  the  neutral  bus  to  the  grounding  resistor. 

Steel  Work. — The  steel  work  for  the  tower  construction  has 
been  shown  in  merely  typical  form  and  the  dimensions  and  spac- 
ings  are  more  than  ample.  It  is  quite  probable  that  a  more 
detailed  design  of  this  outdoor  transformer  and  switch  yard 
would  permit  decreasing  the  height  of  the  structure  and  possibly 
shortening  up  the  width  of  the  various  spans. 

This  drawing,  however,  gives  a  fairly  clear  idea  of  one  manner 
in  which  the  transformers  and  switching  equipment  could  be 
arranged  for  outdoor  service  to  advantage. 

Space  Needed. — As  may  be  noted,  the  tower  construction  for 
the  154-K.V.  installation  occupies  a  length  of  524  feet  on  centers 
with  a  width  of  80  feet,  while  the  corresponding  dimensions  for 
the  110-K.V.  equipment  are  430  feet  length  and  86  feet  in  width. 
The  height  of  the  high  towers  will  be  74  feet  for  use  of  the  154- 
K.V.  installation,  60  feet  for  the  110,  while  for  the  shorter  towers 
these  dimensions  will  be  62  feet  and  50  feet  respectively. 

It  is  considered  quite  probable  that  these  heights  may 
be  reduced  from  5  to  10  feet  as  the  result  of  the  closer 
calculations. 

Cost  of  Building. — With  the  arrangement  shown  of  Fig.  272  the 
space  required  for  housing  the  transformers  and  switch  gear  for 
the  110-K.V.  arrangement  was  320  feet  long,  64  feet  high,  35  feet 


452          SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 


BREAKER  STRUCTURES  453 

wide  or  a  total  of  about  735,000  cubic  feet.  On  the  basis  of 
twenty  cents  per  cubic  foot,  this  would  cost  about  $150,000. 

On  the  same  basis,  the  corresponding  portion  of  the  station 
required  for  the  154-K.V.  layout  would  have  a  cost  of  about 
$225,000. 

The  cost  of  the  steel  work  erected,  and  the  extra  cost  of  making 
the  110-K.V.  A  apparatus  suitable  for  outdoor  service  in  place  of 
indoor  would  amount  to  about  $60,000  showing  a  net  saving 
of  about  $90,000  for  using  outdoor  equipment,  while  for  the 
154-K.V.  proposition  the  net  saving  would  be  about  $135,000. 
These  figures  are  about  13  percent  of  indoor  costs. 

Figs.  273  to  Fig.  276  shows  the  arrangements  proposed  for  a 
typical  220-K.V.  outdoor  switching  and  transformer  station. 

Diagram. — A  single  line  diagram,  Fig.  273  shows  the  main 
connections  proposed  for  this  plant,  that  is  to  contain  4-50,000- 
K.V.A.,  220-K.V.  outgoing  transmission  lines.  As  shown  in 
this  single  line  diagram  of  connections,  each  generator  with  its 
transformer  bank  is  provided  with  a  total  of  three  oil  breakers 
with  suitable  disconnecting  switches.  The  connections  are  so  ar- 
ranged that  while  normally  each  generator  will  tie  in  with  its 
own  transformer  bank,  any  generator  or  transformer  bank  can 
be  connected  to  the  low  tension  transfer  bus. 

Switches  and  Breakers. — On  the  high  tension  side  of  the  trans- 
formers the  electrically .  operated,  3-pole  disconnecting 
switches  are  provided  with  electrically  operated  breakers  in  the 
outgoing  line  circuits.  Normally  each  transformer  bank  will 
be  connected  to  its  own  outgoing  line  breaker  but  by  means  of 
the  electrically  operated  disconnecting  switches  any  transformer 
bank  or  any  line  breaker  may  be  connected  to  the  high  tension 
transfer  bus.  The  disconnecting  switches  were  made  electri- 
cally operated  to  facilitate  their  control  from  one  central  point. 

Plan. — The  plan  view  arrangement  Fig.  274  shows  the  relative 
position  proposed  for  the  transformer  banks,  disconnecting 
switches,  oil  breakers,  arresters,  etc.  While  the  elevation  sec- 
tion 'FF'  shows  somewhat  more  clearly  the  general  relative 
location  of  these  various  devices. 

Section. — The  disconnecting  switches  shown  in  sectional  view 
Fig.  275  have  special  insulator  columns,  each  pole  of  a  discon- 
necting switch  normally  requiring  three  columns.  One  supports 
the  stationary  contact  and  stationary  arcing  horn ;  one  acts  as  a 
brace  pillar,  and  the  third  is  arranged  to  rotate  in  such  a  manner 


454         SWITCHING  EQUIPMENT  FOR  POWER  CONTROL 

as  to  secure  a  vertical  rotation  of  the  switch  blade  and  movable 
arcing  horn. 

As  indicated  in  the  plan  view,  the  two  3-pole  disconnecting 
switches  adjacent  to  the  transformer  banks  have  their  poles 
alternated  and  the  two  poles  in  any  one  phase  have  a  common 
brace  pillar,  so  as  to  reduce  the  number  of  insulator  columns. 

The  disconnecting  switch  located  near  the  oil  breaker  has  each 
pole  provided  with  its  own  set  of  three  insulator  pillars.  The 
disconnecting  switch  used  with  the  arrester  horn  gaps  has  its 
break  jaw  and  stationary  horns  indicated  as  being  mounted 
directly  on  the  terminal  of  the  oil  circuit  breaker. 

The  lightning  arrester  horns  are  mounted  on  similar  pillar 
insulators  and  the  central  pillar  carries  a  combination  horn  and 
transfer  switch. 

Elevation. — As  shown  particularly  in  the  side  and  end  eleva- 
tion Fig.  276  the  oil  breakers  in  the  13.2-K.V.  circuits  are  indoor 
breakers,  these  being  located  inside  the  hollow  platform  on 
which  the  insulators  of  the  220-K.V.  disconnecting  switches  are 
mounted.  These  breakers  are  provided  with  suitable  disconnect- 
ing switches  and  are  arranged  to  tie  onto  a  low  tension  transfer 
bus  or  connect  a  transformer  direct  to  a  generator  as  desired. 

The  low  tension  transformer  leads  in  the  form  of  copper  strap 
are  taken  from  the  transformer  delta  bus  out  through  the  side 
wall  of  the  concrete  platform. 

The  path  of  the  high  tension  connections  from  the  transformer 
terminals  through  the  disconnecting  switches  on  the  platform 
to  the  high  tension  bus  or  to  the  line  breakers  can  be  readily 
followed  from  the  figure. 

The  oil  breakers  contemplated  for  this  installation  are  220-K.V. 
circular  tank  type  breakers. 

While  the  high  tension  disconnecting  switches  have  been  indi- 
cated as  being  operated  by  the  rotation  of  one  of  their  pillars,  a 
somewhat  different  type  of  mechanism  may  be  employed  and 
the  switches  themselves  instead  of  being  mounted  on  concrete 
platforms  may  be  located  on  steel  structures. 

These  various  drawings  indicate  typical  methods  of  arranging 
large  capacity  outdoor  transforming  stations.  Moderate  capa- 
city high  voltage  stations  could  be  arranged  in  a  somewhat 
simpler  manner. 


INDEX 


Air  break  circuit  breakers,  see  car- 
bon breakers. 

Altitude  effect  on  oil  circuit  break- 
ers, 76,  77 

Ammeter  switches,  8,  9,  10 
Ammeters,  see  Instruments. 
Automatic  circuit  breakers,  see  Car- 
bon Breakers  or  Oil  Circuit 
Breakers, 
overload  trip,  88 
protection,  A.C.  generators,  25 
D.C.  generators,  24 
differential     protection,     25, 

167 

exciter  and  field,  24 
feeder  circuits,  26 
motor-generators,  307 
synchronous  converters,  25 
starting,  260,  265 
substations,  G.  E.,  336-343 

Westinghouse,  343-350 
Auto-reclosing   circuit  breaker,   46, 

49,  310 

Autostarters,  264 
Auto-transformer  starting,  264 


Battery  charging  generator  section, 

297 
panels,  296 

and  generator  panels,  303 
and  lighting  panels,  302 
rheostat,  297 

switchboard  assembly,  297 
location,  298 
platform,  298 
Bevels  on  panels,  282 
Breaker,  see  Carbon  Breaker  or  Oil 

Circuit  Breaker. 
Bristol  meters,  176 


Brooklyn  Rapid  Transit  Co.  Control 

Desk,  375,  376,  377 
Bus  arrangements,  406 
Bus  bars,  381 

for  A.C.  service,  381 

for  D.C.  service,  381 

capacity,  383 

compartments,  383 
brickwork,  384 
concrete,  384 
shelves,  384 

enclosures,  385 

extra  high  tension,  388 

fittings,  398 

laminated  type,  386 

material,  382 

open  construction,  388 

stresses,  386,  389,  396 

supports,  394-400 

switch,  401 

systems,  270-273,  382 


Cables,  391 
bells,  404 
bends,  403 

for  auxiliary  apparatus,  391 
for  control  and  instrument  wir- 
ing, 391 

for  dry  places,  403 
for  wet  places,  404 
load  covered,  405 
3  conductor  vs.  single  conduc- 
tor, 403 

Carbon  breakers  acceleration,  42 
attachments,  42-45 
auto-reclosing,  46-49,  310 
bell  alarm,  45 
Condit,  49-51 
construction,  39 
contactor,  71 
contacts,  40 


455 


456 


INDEX 


Carbon  breakers,  current  ratings,  38 
Cutter— I.  T.E.,  51-60 
desirable  features,  37 
distinctive  features,  39 
double  arm,  45 
electric  operation,  41 
electro-pneumatic  control,  60 
field  discharge,  45 
General  Electric,  60-65 
historical,  36 
interrupting  capacity,  38 
inverse  time,  43 
manual  operation,  41 
method  of  operation,  40 
motor  operated  Cutter,  54-67 

G.  E.,  64 
overvoltage,  44 
pneumatic  operated,  59 
relays,  45 
reverse  current,  42 
Roller-Smith,  65-66 
shunt  trip,  43 
signals,  44 
solenoid  operated  Cutter,  57- 

58 

G.  E.,  64 
Westinghouse,  74 
space  requirements,  37 
temperature,  38 
trip-free,  45 
tripping,  42 
underload,  44 
undervoltage,  43 
Westinghouse,  66-74 

Choke  coils,  219 

Circuit  breakers,  see  Carbon  Break- 
ers or  Oil  Circuit  Breakers, 
fused,  33 
Schweitzer-Conrad,  34 

Code  fuses,  28 

Code    rule    for    three-wire    panels, 
314 

Combination  generator  and  feeder 
panels,  304 

Comparison,  indoor  and  outdoor  lay- 
outs, 425,  446 

Comparison  methods  of  three-wire 
control,  314,  315 

Condit  carbon  breakers,  49-51 


Condit  instrument  transformers, 

200-202 

oil  circuit  breakers,  90-107 
Conduits,  404 
Connection,  diagrams, 

ammeter  switch,  10 
automatic   acceleration  from 

counter  e.m.f.,  261 
with  series  relay,  260 

substations,  G.  E.,  338 

Westinghouse,  344 
auto-reclosing  circuit  breaker, 

47 

auto  starter,  264 
balanced  system  of  relays, 

163 

charging  panels  with  magnet- 
ically   operated    switches, 

301 
compensator  connections  for 

regulator,  250 
cutter    three-wire   generator, 

325 
D.C.  starter  with  low-voltage 

release,  259 

double  bus  system,  271 
excess  voltage  protection  for 

regulator,  252 

exciter  and  field  circuits,  361 
face  plate  controller,  257 
G.  E.  voltage  regulators,  243 
generator  and  battery  panel, 

304 

glow-meters,  184 
impulse  gap,  217 
M.G.  sets  for  mine  service, 

307 
motor   operated    circuit 

breaker,  56 

mutually  reactive  coils,  226 
railway,  1500-volt,  D.C.,  335 
ring  arrangement  of  circuits, 

161 

Rio  de  Janeiro,  273 
Schweitzer-Conrad  multi-cir- 
cuit relay,  167 

recording    synchronoscope, 

178 
single  bus  system,  270 


INDEX 


457 


Connection,  Solenoid  operated  cir- 
cuit breaker,  58 
switchboard  A.C.,  440  volts, 

318 

synchronizing,  11,  12 
synchronous    converters    for 

mine  service,  312 
temperature    indicating    de- 
vice, 189 
three-wire  generators,  313 

synchronous  converter,  312 
transfer  type  relay,  166 
typical    generator    and    bus, 

268 
typical  plant  with  sectioned 

bus,  272 

wattmeter  switch,  10 
welding  panels,  316 
Westinghouse    voltage    regu- 
lator, 246 

Connections,  385,  390 
Contactors,  254-5 
Control  desk,  375 

relays,  16 
Controller,  255 

drum  type,  257 
face  plate  type,  256 
Converters  and  M.G.  sets,  328 

D 

Delta-Star  bus  fittings,  398 
fusea,  31,  32 
switches,  19 
Desk,  375 

for  Brooklyn  Rapid  Transit  Co., 

375-377 
for  horizontal  edgewise  meters, 

378 
for    round    pattern    meters, 

379-380 
for    vertical    edgewise    meters, 

378-379 

Diagram  of   connections,    see   Con- 
nection Diagrams. 
Differential  protection,  25 
Direct  control  oil  breakers,  363 
Disconnecting     switches,      17,     18, 

19,  20 
fuse,  30 


Drum  switches,  9 
Duncan  meters,  176 

E 

Edison  battery  charging,  301 
Electric  remote  control   oil   circuit 

breaker,  363 
Electrolytic   lightning   arrester,    see 

Lightning  Arrester. 
Engine  generator  protection,  328 
Esterline  instruments,  176 
Exciter  automatic  protection,  24 

panels,  360 

regulators,  see  Regulators 


Feeder  protection,  see  Protection. 
Feeders  in  automatic  substation,  346 
Field  discharge  switches,  5,  360 

protection,  24.     See  Protection. 

transfer  switch,  6 
Finish  marine,  281 

oil,  281 

Flexibility,  274 

Frames  for  switchboards  angle,  279 
pipe,  279 
small  panels,  282 

Frequency  meters,  see  Instruments. 
Full  automatic,  88 
Fuse  blocks,  switchboard  type,  29 

circuit  breakers,  33 

indicators,  28 

limitations,  28 

switch,  31 
Fuses,  Delta-Star,  32 

disconnection  switch  type,  30 

enclosed  type,  28 

expulsion  type,  27 

General  Electric  type,  32 

National  Electrical  Code,  28 

oil  type,  30 

open  type,  26 

Schweitzer-Conrad,  30 

transformer  type,  29 

G 

General  Electric  Co.,  carbon  break- 
ers, 60-65 
control  switch,  13 


458 


INDEX 


General  Electric  Co.,  disconnecting 

switches,  19 
fuses,  32 

instruments,  175-176 
A.C.    watt-hour   meters, 

176 
D.C.   watt-hour  meters, 

175 
horizontal  edgewise  type, 

175 

round  pattern,  175 
oil   circuit   breakers,    108- 

124 
heavy  capacity  type 

"H,"  114-119 
high-voltage       type 

"K,"  119-124 
industrial,  108 
low-voltage  modern 

"K,"  110-114 
old  "K,"  110 
pole  line,  109 
textile,  109 

Generator  protection,  25.     See  Pro- 
tection. 

Ground  connection,  210 
detector  switches,  8 
detectors,  184 


Hand-operated    remote    control    oil 

breakers,  363 
High-voltage  A.C.  switchboards, 

318-320 

Horn  gap  arresters,  220 
choke  coils,  220 
switches,  20-23 


Inawashiro  control  desk,  379-380 
field  switchboard,  352 
station  layout,  436 
Indicating  meters,  see  Instruments. 
Indoor  station  layouts,  115 
Inawashiro,  436 
44  KV.,  427 
55  KV.,  428-430 


Indoor   station    layouts,    liO   KV., 

430-433 
110  KV.,  Spanish  stations, 

432-434 
110  KV.,  Montana  Power 

Co.,  435 

Influence  switchgear  on  station  de- 
sign, 415 
Instrument  switches,  7 

transformers    Condit,    200-202 
current,  198 
double  secondary,  206 
functions,  198-199 
General  Electric,  202 
makers,  200 
oil  immersed,  199 

insulated  current,  206 

potential,  207 
outdoor  metering,  207-208 

type,  206 
precautions,  199 
relay  transformers,  204 
through  type,  205 
Instruments,  A.C.,  172 

ammeters,  173,  185 
induction,  172 
moving  coil,  172 

iron,  172 
voltmeter,  172 
Bristol,  176 
D.C.  ammeters,  172 

voltmeters,  172 
demand  type,  185 
Duncan,  176 
eclipse,  192 
exploring  coils,  189 
field  ammeter,  173 
frequency  meter,  174,  183 
glow  meters,  184 
graphic  meters,  174,  186 
illuminated  dial,  183 
power  factor  meters,  173 
recording  synchronoscope,  177- 

179 

relay  type,  graphic,  187 
Roller-Smith,  177 
Sangamo,  176 
Schweitzer-Conrad,  177 
static  ground  detector,  174 


INDEX 


459 


Instruments,  static  ground  detector, 

174 
synchronoscope,    177,    182, 

194 

temperature  indicator,  189 
thermo-couples,  190 
watt-hour  meter,  173,  175 
Westinghouse,  179-191 
A.C.  meters,  181 
D.C.  large  meters,  180-181 

small  meters,  179-180 
synchronoscope,  182 
Weston,  192-197 
edgewise  type,  193 
frequency  meter,  196-197 
power  factor  meter,  195-196 
synchronoscope,  194-195 
Integrating  watt-hour  meters,  185 
Inverse  time,  89 
Isolated  plant  switchboards,  326 
I.T.E.— Cutter  circuit  breakers,  51- 
60 


Knife  switches,  1 


Lamp  indicators,  16 
Lead  battery  charging,  301 
Leads  in  structure,  385 
Lightning,  209 

arrester  choke  coils,  219 
condenser  type,  212 
D.C.  service,  211 
electrolytic,  214-216 
gaps,  horn  type,  216 
impulse  type,  217 
speed,  218 
sphere  type,  217 
horn  type,  220 
multi-chamber,  213 
multipath,  211 
non-arcing  type,  212-213 
oxide  film,  219 
Railway    &    Industrial    Eng. 

Co.,  220-223 

Schweitzer  &  Conrad,  222-223 
direct  strokes,  209 
displaced  neutral,  210 


Lightning,  good  ground,  210 

induced  strokes,  209 
Locations  for  structures,  418 
Lockout  contactor,  263 

features  automatic  substation, 

349 
Low  voltage  A.C.  switchboards,  317- 

318,  361-362 

protection  for  battery  charg- 
ing, 300 

release  for  starter,  258 
in  mines,  309 

M 

Marble,  280 

blue  Vermont,  280 
Material,  280 
Meters,  see  Instruments. 
Mining  switchboards,  306 

for  engine  generators,  306 
for  feeders,  308 
for  motor  generators,  307 
Motor  driven  rheostat,  352 

switch,  64 
starters  Condit,  90,  95 

Westinghouse,  130 
Multiple    multipole   breakers,    127, 

133 
switch  starter,  259 

N 

National  Electric  Code  fuses,  28 
Neutral  lead  three-wire  generators, 

326 

Nickel — iron  battery  charging,  301 
Non-automatic  circuit  breakers,  88 

O 

Oil  circuit  breakers  acceleration,  87 

A.C.  control,  85 

altitude  effect,  76 

application,  75,  80 

automatic       recommenda- 
tions, 83 

calibration,  89 

Condit,  90-107 

control  circuit,  86 
voltage,  87 

direct  control,  84 


460 


INDEX 


Oil  circuit  breakers,  distant  control, 
84 

effect  of  regulators,  81 

electric  control,  85 

features,  75 

General  Electric,  108-124 

guarantees,  84 

indicators,  85 

inverse  time,  89 

manual  control,  84 

mechanism,  86 

methods  of  trip,  88 

overload  trip,  88 

rating,  76-78 

series  trip,  89 

short  circuit  curves,  80 

time  of  trip,  81 
relays,  83 

transformer  trip,  88 

Westinghouse,  124-156 
Old  panel  switchboard,  277 
Ontario  Power  Co.,  374 
Outdoor  station  layouts,   22  K.V., 
438-9 

66  KV.,  440-1 

88  KV.,  442 

110  KV.,  443-4 

132  KV.,  444-6 

154  KV.,  446-453 

220  KV.,  453-4 
Overload  protection  battery  panels, 

299 

relays,  see  Relays, 
trip,  88 

Overvoltage  relays,  see  Relays. 
Oxide  film  arresters,  219 


Panel  bevels,  282 

frame  mounted  oil  circuit  break- 
ers, 364 

switchboards  for  D.C.  genera- 
tors and  converters,  321 
Panels,  combination  generator  and 
feeder,  312 

exciters,  360 

1500  volt  railway,  332,  334 

for  three-wire  service,  313 

for  welding,  315,  317 


Pedestals,  372-374 
Plug  switches,  7 

Polarity  control  of  automatic  sub- 
stations, 345 
Portable  substations,  350 

for  motor  generators,  423,  425 
for  rotaries,  423,  424 
Posts,  373,  375 
Potential  regulator,  233-253 

transformer,      see     Instrument 

Transformers. 
Power     control     sections     battery 

switchboard,  299 
factor     indicator,     see     Instru- 
ments, 
switchboard,   General  Electric, 

322 

Pittsburgh  Electric,  323,  324 
Protection      automatic     substation 
against  A.C.  overload, 
348 

D.C.  overload,  348 
low  voltage,  347 
overheating,  341 
overload,  341 
overspeed,  349 
polarity  reversal,  348 
reversal,  341 
reverse  current,  349 
short  circuit,  341 
temperature,  348 
Protection  synchronous  converters, 

331 

three-wire  panels,  314,  325,  329 
two-wire  panels,  329 


Quick  break  switches,  2 


Railway   &   Industrial   Engineering 

Co.,  arresters,  220,  222 
switches,  20-23 
Railway  switchboards,  321 
Reactors,  cast-in,  227 

General  Electric,  226-229 
makers,  224 

Metropolitan  Engineering  Co., 
224-226 


INDEX 


461 


Reactors,  multiple  winding,  230 
mutually  reactive,  225 
porcelain  clad,  225 
semi-porcelain  clad,  226 
three-phase  type,  231 
Recording  meters,  see  Instruments. 
Regulators,  application,  247 

auxiliary  exciter  rheostats,  251 

battery  control,  252,  253 

compensation,  249 

condensers,  250 

excess  voltage  device,  251 

exciter  rheostats,  251,  252 

flicker,  248 

General  Electric  Type,  242-244 

generator,  241-253 

master  relay,  245 

parallel  stations,  250 

rheostat  shunting  relays,  247 

single  operation  of  exciters,  249 

Tirrill,  242 

vibrating  relay,  245 

voltage  adjusting  rheostat,  249 

rise,  251 

Westinghouse,  245-253 
Regulator  feeder  induction,  234 

motor  drive,  237 

no  voltage  device,  238 

outdoor  type,  238 

polyphase  type,  236 

primary  relay,  238 

regulator  limit  switch,  238 

single  phase,  235 

step  type,  233 
Relays,  A.C.  definite  time,  157,  160 

overload,  159 
balanced  system,  162 

type,  162 
bell,  166 

characteristic  curves,  160 
definite  time,  157,  169 
D.C.  overload,  157 

reverse,  158 
double  contact,  164 

high  tension,  170 
multi-circuit,  167 
parallel  system,  161 
ring  system,  161 
series,  168 


Relays,  split  conductor,  162 

temperature,  164 

transfer,  165 
Resistors  for  rheostats,  241 

for  starting,  258 
Reverse  protection  battery  charging, 

300 

motor  generators,  309 
Rheostats,  239-241 

battery  charging,  297 

distant  control,  240 

motor  operated,  240 

resistors,  241 

solenoid  control,  240 

1500  volts,  B.C.,  334 
Roller-Smith  carbon  breakers,  65-66 
instruments,  177 


Safety  code,  295 
Sangamo  meters,  176 
Schweitzer-Conrad  circuit  breaker, 

34 

fuses,  30,  31,  32 
multi-circuit  relay,  167 
Series  trip,  89,  127 
Shipment  of  switchboard,  280 
Short  circuit  characteristics,  79 

curves,  80 

Shutting   down    automatic   substa- 
tions, 340,  347 
Slate,  281 
Standards,  276 
Starters,  A.C.,  263 
automatic,  260 
auto-transformer,  264 
counter  e.m.f.,  261 
D.C.,  258 

electric  operated,  260 
flywheel  set,  266 
mill  work,  266 
mine  motors,  308 
multiple  switch  type,  259 

phase  wound  motors,  265 
series  lockout,  262 
squirrel  cage  motor,  263 
synchronous  motor,  265 
wound  rotor  motor,  263 


462 


INDEX 


Starting      automatic      substations, 

General  Electric,  339 
Westinghouse,  343 

combinations,  308 

converters  from  A.C.  end,  332, 

357 
from  B.C.  end,  330 

switch,  332 

Station  layouts,  see  Indoor  Station 
Layouts  and  Outdoor  Sta- 
tion Layouts. 
Supports  for  tubing,  390 
Switch,  ammeter,  8 

control,  12 

Delta-Star,  19-20 

disconnecting,  17-20 

drum,  9 

field  discharge,  5 

field  transfer,  6 

front  connection,  3 

fuse  shunted,  32 

fused,  31 

galleries,  419 

General  Electric,  19 

ground  detector,  8 

house,  418 

horn  break,  20 

instrument,  7 

knife  type,  1 

motor  starting,  5 

Plug,  7 

rear  connection,  3 

safety,  6 

synchronizing,  9,  11 

voltmeter,  8,  11 

wattmeter,  11 
Switchboards,  A.C.,  286 
blank  panels,  362 
connections,  267 
with  knife  switches,  317,  361 
oil  circuit  breakers,  319, 363 

A.C.  instruments,  293 

ammeter  scales,  291 

angle  iron  frame,  279 

battery  charging  sectional,  296 
bevels,  282 

bracket  instruments,  294 

bus  taper,  288 

carrying  capacity,  289 

copper,  289,  290 


Switchboards,  D.C.,  286 

connections,  267 

electrically  operated,  351 

heavy   capacity   Al.    Co.    of 
America,  353,  354 

instruments,  293 
desks,  288 
diagrams,  267 
direct  control,  284,  287 
distant  control,  287 
double  bus,  271 
early  panels,  282 
electrical  control,  287 
equalizer  bus,  290 
exciter  bus,  290 
feeder  instruments,  294 
field  ammeters,  293 

and  exciter,  351 
flexibility,  274 
Ford  Co.,  355-357 
frame,  282 
General  Electric  D.C.,  323,  355 

panel  sections,  283 
ground  detector,  294 
Inawashiro,  353 
indicating  wattmeters,  293 
instrument  transformers,  270 
instruments,  see  Instruments, 
interrupting  capacity,  292 
largest  builders,  274 
location  of  bus,  289 
marble,  280 
marine  finish,  281 
material,  280 
mining,  306 
oil  circuit  breakers,  292 

finished,  281 
old  panels,  277 
panel  rating,  291 

sequence,  288 

type  G.  E.,  366 

Westinghouse.  365 
panels,  288 


pipe  frame,  279 
posts,  288 

present  standards,  278 
ratings,  292 
remote  control.  287 
requirements,  286 


INDEX 


463 


Switchboards,  rheostats,  294 
ring  bus,  271 
Rio  de  Janeiro,  351 
safety  code,  295 
sectioned  bus,  272 
shipping,  280 
single  bus,  270 

line  diagram,  267 
slate,  281 

vs.  marble,  281 
small  panels,  281 
special  bus,  273 

panels,  285 
standard  panels,  285 
standards,  276 
switching  apparatus,  292 
temperature  rise,  291 
truck  type,  368-370 

construction,  369 

contact  jaws,  370 

covers,  370 

interlocks,  370 

limits,  369 

mounting,  370 

tubing  carrying  capacity,  290 
typical  connections,  268 
ultimate  bus  capacity,  290 
wooden  board,  276 
Synchronizing  switches,  8 
Synchronoscopes,  174,  182,  194 
Synchronous  converter  stations,  422 


Temperature  relays,  164 

Thermostat,  349 

Three-wire  Cutter  breakers,  325 

control  electrically  operated, 

325 
Time  element  for  starting  breaker, 

309 

Top  connected  breakers,  420 
Torque  compensator,  160 
Transfer  relays,  165 
Transformer,    current,    see    Instru- 
ment Transformers, 
fuses,  29 
panels,  331 

potential,  see  Instrument  Trans- 
formers, 
trip,  88,  127 


Tripping,  calibration,  89 
Truck  panels,  368-370 
Tubing  for  bus,  390 

U 

Underwriters  requirements  for  wir- 
ing, 391 

Union  Electric  Light  &  Power  Co., 
372 


Voltage  readings,  A.C.  panels,  364 

regulators,  see  Regulators. 
Voltmeter  switches,  8,  11 
Voltmeters,  see  Instruments. 

W 

Walker  isolated  plant  switchboard, 

326 

Watt-hour  meter,  see  Instruments. 
Wattless  component  indicator,   see 

Instruments. 

Wattmeters,  see  Instruments. 
Welding  capacities,  316 
panels,  315 
processes,  316 
Westinghouse  carbon  breakers,  66- 

74 

control  switch,  14 
instruments,  179-191 
oil  circuit  breakers,  124-156 
brush  contacts 

type  B,  130-134 
C,  139-141 
CO,  145-147 
E,  134-139 

0,  141-145 
Butt  contacts 

type  G,  147-156 

H,  129 

knife  contacts 
type  D,  124 

1,  124 

multiple-multipole,  127 
wedge  contacts 

type  F,  126 
regulators,  245-253 
Weston  instruments,  192-197 
Wire  and  cable,  402 
Wooden  switchboard,  276 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 

Los  Angeles 
This  book  is  DUE  on  the  last  date  stamped  below. 


DEC  1     1958 
NOV  11 


6  R£CO 

1960 


2  6 


SEP  5      REDD 


KOV  2 


211966 


yon  1  6 

JBI13RBS 


MAY  2  8  1969 

WAV 


Form  L9-lCOm-9,'52(A3105)444 


Library 

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